I know you are just a parent like me, but you've been the chief advocate for DPL on this forum for a while now and your need to address my question with "whataboutism" is telling.
Plus your statement is incorrect. It wasn't SCDSL "teams" that left CSL, it was "clubs." By contrast, the DPL clubs that were playing for SCDSL and CSL are still there. They are just keeping their B teams out of league play, having them play a reduced number of fall games in a round robin format and calling it a "league." The situations are not parallel.
Most of the DPL benefits you've cited appear to be benefits that come along with being a B team in a large club (good training, the chance to perhaps be promoted to the club's A team some day, playing in good tournaments, getting games videotaped, etc.). Other benefits (being able to play at Silver Lakes each week) seem like detriments (there are no home/local games so there is increased travel).
The only clear benefit I see to clubs from playing in DPL specifically is that the lesser DPL teams are guaranteed the right to play against the good DPL teams and lose to their hearts content without the threat of demotion. While wins/losses shouldn't necessarily be the top priority, our girls should be playing similarly-talented competition to the extent possible, especially at these older groups. This is why the vast majority of club soccer leagues in this country allow less talented teams to be moved to a lower division, or promoted, as warranted. But the structure of DPL doesn't permit that to happen. There are some really good teams in DPL, but they are stuck, now and forever, playing whatever the other DPL clubs are able to throw at them.
If there is anything that ends up breaking DPL apart, my guess is it will be that. At some point, for example, Legends might get tired of blowing out other DPL clubs all the time and will seek an arrangement that will give them a chance at more consistently strong competition.