Blocking is a lot harder than it looks especially when there's distance and unfavorable angles between you and a rusher. You can't hold, you often have no forward momentum on the line (in contrast to a rusher), and you can't hit from behind. If you get juked or turned the wrong way, the rusher is gone.

A TE is a generalist, an average blocker in most cases, and is often blocking in this unfavorable context.

That said, his blocks during the Super Bowl were especially weak and his behavior made it look like he got embarrassed (or rocked) by Sweat early in the game and lost confidence. Sweat is also the best player in that position in the league (afaict ... based on this one game I watched) so he probably makes everyone look like a fool.

Edit: looks like other people have chimed in who actually know the player