We can only speculate on the why part

Based on experience, even asking Rashad Muhammad and Darryl Gaynor II directly about their departures wouldn't necessarily generate the actual reasons why.

So we can only truly speculate.

But this factor seems a good bet, at least for Muhammad. He saw another struggling season coming up for his junior year, another five or so win record and made the calculation it was not worth it to continue here. Really, who can knock him?

Other possible elements:

He was pretty much given free reign on the court as a freshman and sophomore because, aided by his length, he was about the only player who get a semi-decent shot off, especially when the shot clock was winding down. That had to be attractive.

But there wasn't really another player on the team to challenge him in practice, to force him to dig deeper, to expand his skills set. However, maybe such is giving him unearned credit.

Maybe he desired more talented teammates, ones who could draw the defensive focus away from him.

Possibly he determined that SJSU or even the Mountain West Conference wasn't where someone with his self-perceived ability/potential should be performing (although that obviously wasn't present during his recruitment process unless he felt he settled -- but why wouldn't he have then left after year one?)

I'd go with the initial suggestion as the primary factor.

With Gaynor, it's a bit harder reading the proverbial tea leaves.

He received much more playing time than he would have anywhere else as a freshman (24.3 minutes a game, 21 starts). His amount of on court minutes likely would have lessened considering the return of Jalen James and the addition of Gary Williams Jr. But my sense is he was also being asked to modify his game, to make better on-court decisions with the ball and to shoot less and with greater intelligence and didn't react well.

College of Southern Idaho (his new home) is a national junior college, one with a very well thought of basketball reputation (usually 5-6 players on the roster any year go D1, some fairly high). The odds for playing time will be better there. Maybe the losing loomed as a reason but only time will tell if being in Burley, Idaho rather than San Jose turns out to be the better situation for his basketball future.