You also have to keep in mind that many, MANY high school teams have coaches without proper training, credentials, or even with no cheerleading experience at all. I learned that firsthand working UCA camps last summer. Coaches will want their teams who just hit a jank lib for .4 seconds to immediately start working full ups way more often than one would expect...and many of these coaches are ones who get "cool new tricks" to try with their team from YouTube videos and Bring It On.
The removal of double downs was smart -- it prevents a lot of injuries that I know have happened due to insufficient progressions. I know that many teams CAN safely execute this skill, but unfortunately many school systems and athletic departments require all coaches to come from the school faculty and/or just don't really care about the cheerleaders, which makes finding a skilled coach difficult.