No matter how good you are at something, you may not be employed to do it. Some NBA teams have to use the same logic.
Employers don’t strictly look at your capabilities. They’re also looking at their own needs. If they already employ the best person for your job, and it’s a one-person job, they’re not going to hire you.
They may have a great player, but if they’ve got two better players ahead of them in their depth chart, they may not give them the starting job. It’s the nature of the business.
For example, look at Naz Reid of the Minnesota Timberwolves.
He looks like a starting-caliber big man, but with Rudy Gobert and Karl-Anthony Towns ahead of him in the depth chart, he’s not going to get the opportunity to prove it.
Would he find a better opportunity with the Miami Heat?