One of the really weird things with bikes is that entry level bikes tend to be 3x7 which means that you have a lot of extra weight and complexity (a second shifter, shift cable, and front gears) for pretty much no benefit over a 1x9 system.
>The first thing to go on my bike is the deraileur though, they keep a year or so even if taken care of
>I do buy the cheapest ones I can find for around 10-15 euro
Single speed and 3s chains last 5000km easily while 12/13s won’t last much more than 1000km.
in some number of years, 3x parts will become less available and less common on cheap bikes.