why is it that almost all cars nowadays have orange peel?can the manufacturer do something about it?
It's a consequence of depositing paint as a spray/mist. When I was reading up on this, there are apparently a bunch of factors that affect the degree of orange peel. The nozzle, distance, velocity, temperature, additives, etc. It's also allegedly more of an issue with today's water-based paints.
Once the factory picks all its settings, since the paint spraying is done by computer controlled robotic arms, it's suppose to be very repeatable from car to car. So, if the hood has slightly less OP than the doors, that should be the case on all of that model car painted on the same line (until someone changes some setting or the paint mix).
There are even orange peel measurement instruments so they can monitor consistency (they cost about 30-80 grand so not a DIY instrument):
https://www.byk.com/en/instruments/products/appearance-measurement/orange-peel-doi-meter.html
Short of wet sanding the entire car after the paint has cured (and 99.9% of car owners would not be willing to add this cost to their car), there's going to be some degree of orange peel.
A couple other interesting thing I read (but take these with a grain of salt since I'm not sure how "official" the source was):
1) auto manufacturers don't seek to minimnize OP because it can help mask minor defects in panels such as spot weld marks.
2) "Leveling" additives can be added to make the orange peel less visible once it cures, but the consequence is a softening of the paint.