I kind of see it this way, Sochan was important when the team didn't have a whole lot of talent. He was a pick that filled a need. Slowly, through the draft and through trades the overall level of team talent improved. Bryant was drafted for a need as well, but took a lot less time to show his potential- and the spurs like what they see.
The team was hoping Sochan would improve also but instead he regressed to the point, for what ever reason, he basically became unplayable in this system. If you don't improve or at least keep up, you are history in the NBA. Its some other teams turn to invest in Sochan. Maybe it works out for him, maybe not.
Doesn't matter any more , the spurs have moved on. Time to look forward not backwards.