Why do perimeter players get easy foul calls while bigs get hacked in the paint with no whistle?

This has been a thing for years, but I have been noticing it more and more now. I am mostly talking about non shooting fouls where other players can hack and get away with way more physicality on bigs in the paint without getting foul calls. And perimeter players on the other hand are generally able to get foul calls much easier and more often than bigs on ball and off ball. Like if another player reaches in on the perimeter player like Austin Reaves, SGA outside the 3pt line or holds them slightly when they are moving off ball it will instantly be called a foul even if there is "marginal contact". However when big players like Jokic, AD, etc get mauled in the paint off-ball, shoved on ball or even off ball, and players are reaching in like crazy it oftentimes won't even be called a foul.

So I am just curious as to why that is the case? An example would be AD guarding SGA on the perimeter and instantly getting called for a foul for barely even touching him or slightly reaching in, but when SGA is guarding AD on a post-up he can get away with 10x more physicality on defense, reaching in, pushing, and shoving AD without getting called for a foul.