But in most cases you can take one level out of ID or IS or RB and replace it with two or three SB levels, keeping the salary constant (so it's clearly the cheapest inside skill). When it comes to those 2-3 extra possessions per game that you can get by doing that, many believe that also the threat of blocking is a major factor of a team's inside defence. However, there's no evidence for that (at least that I'd know of), so it will for now stay as speculation.
rubbercube
People aren't willing to put in the effort to train passing and handling for the most part for their big men and they're frittering away quite a few possessions indeed with needless turnovers. I did a quick TL search for 15 ID, there are 312 players - and only 31 with handling and passing at even 6, and a mere 3 with passing and handling at 8 (but 81! with passing handling at 3 or less).
If people aren't willing to change their behavior when the evidence of lost possessions is right there in their faces and in their three-skill tree's stat line, there's no reason at all they're going to change for something that isn't spoon fed to them.