A typical car might have 2.5 bar tyre pressure, and use the Schrader valve system.
A typical mountain bike might also have approximately the same tyre pressure, perhaps a bit more, and also use the Schrader valve.
Why is it that a car tyre seems capable of maintaining most of its pressure after a year, while a few weeks might be enough to notice a significant difference in bike tyre pressure?
There are other related questions here, such as:
Do tire / tube / valve combinations that don't leak air exist?
How long should a road tyre hold its pressure?
These questions have answers that discuss how air can leak mostly through the rubber itself, but also in the valve system.
This only brings me back to my own question: Is the rubber that different on a car? Are there any tires I can get for my bike that will not leak? I'm sure I'm not the only one that finds it annoying to maintain the bicycle tire if there is really no need for it with the right kind of material properties and valve systems to prevent that. When people can justify spending large sums on relatively minuscule gains, why not more of a focus on maintenance free tires?