I clean & lubricate the chain every few weeks.
I don't know how much you ride per week, but you should lubricate the chain only when it starts squeaking. For me, that's bit over 800 km. When it does start squeaking, there's no time to wait, the squeaking and chain wear will accelerate so quickly that even when it makes the slightest squeak, you need to lubricate it at that point of time without waiting.
I have put 3675 km on my chain, and it has been lubricated probably three times apart from the factory lubrication. I just recently did the last chain lubrication out of those three.
I measured my chain with a 0.5% wear tool (Shimano TL-CN41). It didn't show 0.5% wear but was very close to it, because if I reduced the chain tension a little I managed to fit the go/no-go gauge in (it should be used with full tension). I measure it every time I lubricate it, so this means the next time the chain starts squeaking at about 4500 km, it probably shows it's worn.
So with good chain lubrication strategy, you get 4500 km out of a chain, if you use the 0.5% wear mark. Some tools also have a 0.75% wear mark but this comes with an increased risk of sprocket wear.
The reason chains are replaced is that if you replace it early, you don't necessarily have to replace sprockets and chainrings every time. But how many chains can you wear for a sprocket cassette? I don't know, maybe 2, maybe 3, maybe 4. But I expect at least 2.
My chain lubrication strategy is as follows:
- I never remove the factory grease. It's the best lubricant.
- I only lubricate the chain when I can hear the slightest amount of squeak.
- Before lubricating, I check the chain with a Shimano TL-CN41 gauge. Only Shimano TL-CN40, TL-CN41, TL-CN42, Park Tool CC-4 and Pedro's Chain Checker Plus and Pedro's Chain Checker Plus II are accurate because they are the only tools that measure using three points, not two (so they tension the chain), meaning they only measure pin wear and not roller wear, roller diameter and roller clearance.
- When it's squeaking a bit, it's almost free of oil. Then I remove the dirt by first alternately using a specially reinforced paper towel (ordinary paper towels won't work) and two stiff brushes. You can't get it fully clean this way, removing it from the bike would allow more thorough cleaning at the expense of more time needed (and maybe a new specially reinforced connecting pin needed), but the extra time would cost so much it doesn't make any sense if receiving any significant amount of salary from your dayjob, considering how cheap chains are. A on-the-bike chain cleaning machine could work, but it makes a huge mess where you use it, so using it on your own property doesn't make sense and using it on someone else's property would probably be a crime due to the horrible mess it makes. And also disposing of the environmentally damaging dirty cleaning fluid ain't nice.
- When the chain is reasonably clean, I add thixotropic motorcycle chain lubricant in a spray can, first shaking the can before applying. I never use any other type of lubricant, in particular I never use so-called "dry" lubes. Don't fear the spray mechanism, the lubricant is so thick it doesn't ruin your rim brake tracks (if running rim brakes).
- After the chain is fully lubricated (one run around it is enough), I remove the excess lubricant by using a clean specially reinforced paper towel. When the chain is reasonably free of excess lubricant, it's done. I never touch the chain again until I can hear the slightest amount of squeak.
It takes about 20 minutes to clean and oil a chain on a bicycle work stand with these procedures. Most of the time is cleaning, second largest time consumer is removing the excess oil, the simplest task is adding the oil.
About chainrings, I understand that Jobst Brandt had a 300 000 km 50-tooth chainring that was about worn. So you get as much life out of a big chainring as you would get from a car engine. That 300 000 km chainring though was rotated (5-bolt attachment) several times during its wear life, if using a modern ring with shifting aids this may not be possible, but 100 000 km should be possible at least. That's assuming you always replace your chain early and use the highest quality 7075T6 aluminum chainrings.