I have an almost brand new decathlon rockrider st520 (bought it 3 weeks ago) and noticed if I preload the bike the suspensions just don't compress. They will compress only if you hit the front brake and push down on the handlebars. I got it for my birthday and I use it just to cycle around my town and go to school, so I don't go on trails. My friend has the older rockrider 520 and his suspensions compress way easier even while you're on the bike. Also, the bike has a weight adjuster for the fork and nothing else. Could it be a problem of the suspension or is the bike just made like that?
There are many factors affecting the behavior of a suspension fork that may be in play. Let me describe those that I can recall and which can explain the difference between the two identical bikes (one older, one newer).
Many (if not all) suspension forks have a "break-in" period in the beginning of their service. During that period of riding, the fork gradually "loosens" as its internals start to play with each other. I definitely felt such a break-in on my new fork. Some manufacturers list the length of the break-in to be as long as 50 hours, which I think is an overestimation.
The bicycle in question is at the lower end of price and quality ranges, and so is its fork. It may happen that characteristics of such forks simply vary wildly across the production batches. By a pure (bad) luck, your friend got a softer fork, you got a stiffer one.
While such entry level forks are not very configurable, there may still be some adjustments that affect the feel and dynamics of the fork. In this case, these two forks are simply set up in a different manner, and it should be possible to try doing some adjustments. More advanced forks typically have a few tuning knobs that allow to configure air pressure, compression and rebound.
You and your friend are in fact built differently (weight, height), and so are the seemingly identical bikes (frame size, frame geometry etc.). Same named bike models, if they have different model years or are from different production batches, may in fact have different components. Two forks looking identical on the outside may have different internals.
Finally, a fork that is slower to compress does not mean a worse fork. A suspension that compresses too easily can result in the front end of the bike being lower more of the time, which is not optimal. The tune of the fork depends on the riding circumstances and rider preferences. Many pros run their suspension very stiff because of the terrain and speeds they deal with.
My advice would be to continue using the bike with the fork for a while (a couple of dozens hours of riding). If you are content with the feel it gives you after that, just keep it as is. Otherwise, you may play with the tuning it has, but be sure not to wreck it in the process (do not unscrew things all the way out!). It is unlikely to make any difference however, I am afraid to predict, but I may be wrong.
If you are still not content with it, your best option would be to look for a better fork, or a better bike. In the urban setting and without any tricks involved, I do not think that you'll be at a disadvantage with your current whip.