Yeah, there's a hidden stat called fouled% that we can't see that has something to do with it.
However, this is pretty much fact at this point: Players with a large number of free throw attempts often don't end up anywhere close to their RL total, while players with fewer ftas end up much closer or often exceeding said total. If you run lower total usage, you will see the ratios start to line up more closely, but you're losing games at the expense of trying to achieve a real number. Don't do that. Just accept that Steve Nash & James Harden go to the free throw line about the same number of times and that Harden at least is a better defender than Bill Russell ever dreamed of being.