Why Don’t Teams Play 6 OL instead of 5 OL and a TE More Often?

This might be one of these things:

Hey, why didn’t Grizzly Adams have a beard?

Grizzly Adams DID have a beard.

But why don’t teams play 6 OL more frequently? Is it against the rules? I feel like I see it all the time in the red zone, but why isn’t this strategy explored more often? Do you remember the team from 2015 that had to have their terrible-blocking/decent-pass-catching TE in to block for a majority of the year? Why didn’t we just play an OT there instead?

Say we lined up 2 TE’s and 2 WR’s, except one of the TE’s is an OL. The defense knows that the OL is very likely to not run a route, but how much of a detriment is that? They still don’t know if it’s going to be a run or a pass, extreme down-and-distance notwithstanding - they just know that one particular player won’t go out on the route if it’s a pass. Say they see the OL lined up TE, do you shade that side because they might run that way, or do you shade the other way because you think they’re going to pass? What if you’re wrong?!?!

In other words, although on this type of play you lose one eligible receiver (not literally, but it’s very unlikely you send an OT to run a route other than for extreme deception that you can only use a time or 2 during the season to truly be effective), can defenses really hone in to take advantage of it if they cannot reasonably predict run and pass? How aggressively can defenses play such a formation without leaving themselves vulnerable?

And I’m certainly not suggesting to reinvent the wheel. Base formations work for teams for a reason, but I’m simply curious why the 6 OL isn’t explored more from a sub-package standpoint.