Are young NBA players less polished defensively than young MLB players?

I don't have a source to back this up but I've started to observe something. It seems like on average, MLB draftees (position players) are fairly polished defensively when they enter the league. Like they are drafted at SS/CF/C for a reason because they were the best defensive shortstop against their competition. It's only hitting that needs work the most.

Yet with NBA players, it almost always seems like nobody is really polished defensively. Like you hear so many speculations and doubts about how they can play defense at an NBA level.

Why is that the case? How come it seems like MLB players are taught how to play good defense while NBA players aren't really taught that until a few years into their career?