Default [Q] Chipset support for new roms

So I'm not a developer or anything, just an enthusiast.
I was wondering something.

ROMs often don't get updated because support of the chipset has been dropped. I'm guessing this is like a driver?
If it's the same hardware, why does it need a new one? What changes in each new version of Android that means it needs a new one?

Also for those that have lost support, some devs still make ROMs. How? Do they make one themselves somehow?

I'm going to look really stupid if this is wrong.

Thanks!


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