I'm sure you saw how the Clips defended him in the 2nd half. They had a guy superglued to him at all times. Absolutely no breathing room. Plus they had a strategy where they clearly tried to wear Lauri down by relentlessly bumping and grabbing him every time he tried to relocate or post up. Looked like a wrestling match out there. Hey, if the refs allow it, it makes sense.
Markkanen still found some mismatches near the basket, sealed his guy and asked for the ball, but at this point in his PG "development" Sexton simply can't throw that entry pass. You can see him hesitating and wasting time, until the moment is gone and the passing lane closes. Olynyk is pretty much the only one we have (besides Conley) who can execute those passes.