This was Hextall's decision, don't try and deflect the blame.
Hextall is conservative with player development (not crazy conservative like some would claim, but a bit cautious), and Myers is relatively inexperienced and doesn't look like he's really comfortable out there right now.
Just look at Vorobyev, same age, also relatively inexperienced, but his instincts are off the chart, every time you look up, there is #46, making a subtle little play to steal the puck, get in the way of a pass, make a nifty little move to retain possession, etc. That's what a NHL prospect should look like. Not the flashy play which is pure athleticism, but the little plays that show you he understands the game and can anticipate what is going to happen next instead of always reacting and always be a half step behind.
Other players need that year or two in the AHL so those decisions become second nature and they can just play and use their athleticism without constantly facing paralysis by analysis, thinking too much instead of playing instinctively, pressing instead of going with the flow of the game.