There’s a balance.
If you have a “big” PC with tons of case fans and no ducting (so all the hot air just circulates around inside), it’s going to be noisy, no matter how fancy your case fans are GPU are. There are just too many fans, and most of them are trying to get the inside of the case reasonably close to ambient temps.
If you have a mini PC with a laptop fan, it’s just too small, so it has to spin very fast.
The “sweet spot” is SFF builds that duct everything, and throttle the parts. If you have 1 heatsink fan and your GPU sucking in ambient air, and you undervolt them, they’re near silent.







The real answer is because it’s default.
People use what’s the default. It’s that simple. Any knowledge of how images are encoded is kind of unnecessary information for most folks.
There are a ton of technical and usage-based arguments around image formats, and political complications, but ultimately jpeg’s eternal dominance comes down to people using their app defaults, and wanting stuff to just work. And PNGs are big enough to create technical issues or incompatibilities, sometimes.