I remember, as a kid in the seventies we were able to ride blocks without ever touching the handlebars. Today, I only see road-bikers riding without hands - and this is rarely. I almost never see hybrid or mtb bikers go without hands.
What happened? Is it because I got older that I don't have the sense of balance anymore? Or are bikes made differently in the sense that they're not self-balancing? Or is it the forward positioning??
Nothing happened or changed. It's just your observational bias coupled with different demographics preferring different bike capabilities.
Many children's bikes have relatively relaxed geometry, which makes them stable which has benefits for kids. Bikes built for adults usually aren't as stable, because stability and maneuverability are at odds with each other, and the adult riders want the maneuverability.
Mountain bikers value fast handling over stability, and so do many road cyclists.
However, many triathlons or time trials are events where maneuverability is not important, so many of those frames are much more stable. Touring bikes are also in that group.
I have a bike built up from a nashbar touring frame, that is so stable I can nearly fall asleep while riding. I hop off that bike and hop onto an 80s Bianchi racing bike, and trying to ride no-handed at any speed less than 35 mph (55 km/h) is virtually an instant crash. My surly cross check is in the middle of that range.
I think there's a large element of selection bias, combined with changes to roads and traffic rather than bikes.
When you were a kid you used to ride with kids who rode a lot, probably on fairly quiet roads. Kids probably ride less than they used to, especially on roads with traffic. Now you ride as an adult, you see fewer kids riding, and pay less attention to them. You're probably riding busier roads - traffic has increased in many places; on top of that you're likely to be riding a direct route to get somewhere. On the other hand for training, racing or social rides you're likely to be going a long distance on unpopulated roads,while your riding partners (if any) get on with riding - in even a loose group you haven't got much margin for error.
On the bike paths round here I regularly see people riding no hands; neighbour's kids do too. There are also people riding on the pavement (or sidewalk, it's illegal to ride there whatever you call it) no hands, but much more rarely on the roads.
I bet you also saw a lot of wheelies when you were a kid too, and don't see many of those any more -- it's the same effect.
The biggest influence on how a bike steers is 'trail'. Trail is the distance that the contact area of the front tyre on the ground trails behind a line drawn through the steering axis to the ground. (see the Wikipedia on bike geometry)
It would be interesting to find if 'trail' lengths have changed over time, and thus the ease of riding hands-free has changed.
Look Ma, no hands!
Look Ma, no feet!
Look Ma, no teeth!
The point is, you cannot ride a bike without touching at least one more point than your saddle. When you ride without hands, that second point is your feet. Lose the pedals from under your feet, and disaster is unavoidable. You won't be able to do anything about it. You won't be able to grab the bar, you won't be able to brake (the brake levers are on the bar), and you won't be able to steer.
If you happen to be heading into a moat, you'll go into the moat.
If you happen to be heading for a wall, you'll go into the wall.
If you happen to be heading at a truck, you'll go into the truck.
You are just a passive passenger on your way to disaster.
When you ride without hands, your pedals are a single point of failure. Thus, you are risking your life for absolutely no gain.
Now, road racers click their feet into their pedals. This allows them to pull the pedal up at the back stroke, but it also makes their connection to their pedals much more failsafe than when you ride without this feature. If you do not have this extra safe connection to your pedals, don't ride without hands.
So, the best possible answer to your question would be: Because riders have wised up and learned to avoid this needlessly dangerous behavior. I don't know whether that's actually the case, though.
Ps: I learned this the hard way, including four weeks on crutches. Even a quarter century later, this accident still scores as my worst accident ever. Please learn from my experience instead of making your own.
Besides the variables mentioned in the other answers, most importantly trail, i.e., the distance between the points where the steering axis crosses the ground, and where the front tyre touches the ground, there are a few further key variables. Larger wheels with heavier tyres have both more rotational inertia, essentially acting like a big gyro that stabilises the ride, and also higher damping through losses in the rubber, which has a further stabilising effect. Just putting heavier tyres on the same bike can make it easier to ride it hands-free (and heavier tyres are obviously counterproductive if you want to go fast). And then there is the location of the handlebar and everything attached to it with regard to the steering axis: a long stem that brings the handlebars way forward of the steering axis stabilises and makes it easier to ride hands-free, while a short stem together with handlebars angled backwards makes it harder.
I have wondered about this for years after buying/riding many modern bikes,
The answer above relating to 'trail' or castor angle seems very logical, early BSA 26" mens bikes had curved forks putting the rider further back from center of of wheel, in addition the handle bars where much wider and centered close to stem.
Modern mountain bikes tend to have the rider more over front wheel head down position, forks can also have shocks which work better with straight forks.
Here's the best image I could find quickly, note the seat/handle bars way back.
Thanks for posting, been wondering for ages - now know what to look for !
