Replying to
@Soy_Magnus@clew.lol they make a drywall primer called PVA primer for $8/gallon but it takes about 3-4 coats to get solid coverage because there is such low pigment in it.
There's a lot of chemistry that goes into painting but no one gives a shit so JUST SLAP IT ON becomes the default. But usually you can save a lot of time/material with the right product.