Exactly.
If my 7'3 center (or even my 6'9 pf for that matter) would be able to dunk after an offensive rebound i would do just that, unless of course we need a 2. However, in this game the presence of one 6 footer next to me is enough to make my guy go into a weird/unnecessary contested layup that usually misses. THAT is why most rebounders kick it out.
Also, about posting up. Most don't do it because they immediately get stripped/doubled when they attempt it. Not because they don't want to score...
Finally, not every rebounder stands under the rim cupping his privates. Personally i move around a lot, setting screens and flashing to the basket. I even post up from time to time. Either way, as much as i dislike those who do it, it's 2k's fault for not implementing def/off 3 seconds and making that screen animation impossible to box out against.
And for the love of all that's holy, please 2k give us the ability to box out people who are standing behind the backboard to avoid the 3 sec in the rec.