Yes, yes there is something “stopping them from trying OTS”. Let me explain.

Example 1. Aviate. Twelve year United Express guy. Spring 2019 waiting for a CPP interview. Was told the program was being redone and to wait for interview invite in new program (Aviate). Waited until Fall of 2019 when Aviate interviews started. Interviewed. Got the Yes. The program requires an additional 6 month wait to transition to United. (In addition to hour and time commitments already completed). That led right into Covid. Waited another 15 months for classes to restart. Hiring starts. CPP pilots started in June. As of now, no Aviate pilots have been invited to Class. Still waiting.

Example 2. OTS. Interview in May 2021. Start class 3 weeks later.

What you are saying is get out of the line Example 1 guy has been in since the Spring of 2019, and start over trying to get a spot in the other line? And how likely do you think it is to get an interview invite if you are an Aviate pilot who steps out of line? So, yes, there is something “stopping them from trying OTS”.

The bottom line is - some guys are trying to determine whether the Aviate program is their best option. For an experienced guy, it probably isn’t. If United is your goal airline, it’s probably best to go to a non-United regional or LCC. It is unlikely United will cannibalize from their own feed, when they can get pilots elsewhere. Just my 2 cents.