just to be clear, the USAG XCEL program developed from other programs that were already in place in a few regions. Many states developed programs to specifically supplement the JO program - to encourage compulsory girls to compete optional routines in the off season and to give an alternative for between-level for girls not ready for the next level (most often L7), and yes, for girls/gyms who didn't want to go the compulsory path. The programs were literally called "prep-op" as in prepare for optionals.
So no, the original purpose was not a less intense program. It was a supplemental program. Even once USAG began to nationalize the program, it was still touted as a supplement for compulsory gymnasts in the off season. It was only a few years later that it transformed into a completely separate, less intense program. Of course, USAG had planned this along but had to do it in steps over several years, including the change in JO levels with the addition of a mid-range L6 to decrease the cross-over of girls who aren't quite ready for 7. The areas where you see the most XCEL-to-optionals, are the areas that had strong prep-op programs before USAG took over XCEL. These areas were essentially forced to adopt the name and rules, for national continuity, but some gyms continue to prefer to follow the prep-op to optionals path because it works for their gymnasts. Dd went through prep-op just before Xcel was formed nationally. I don't think she/we would have stuck it out in the early years if she had to go the compulsory path, but she had enough talent to get to L10 and I am grateful that we had the option of an alternate path that helped to get her there.