We have Little League as our local rec league, and we have kept rec league and travel teams strictly as separate entities, even though we have players that participate in both. My DD played both from 10U to 12U. She played LL because that is where all of her school friends were, but she enjoyed the competition in TB much better. After 12U, most of her school friends stopped playing softball altogether, so the draw for rec league really wasn't there for her, so stopped playing LL after Majors (12U). It's a fairly common and natural progression.
There are some Little Leagues that form travel teams specifically to get better for the LL tournament at the end of the year, hoping that they get to the LLWS. Those types of teams have to have their players play in the rec league games because of the participation requirements for the LL All Star teams and tournaments. Those are the leagues that I see where the rec league tends to sustain itself in the younger age groups. But after 12U, I usually see them fall apart as well since the best players go to better TB teams, and the other girls lose interest.
There are some Little Leagues that form travel teams specifically to get better for the LL tournament at the end of the year, hoping that they get to the LLWS. Those types of teams have to have their players play in the rec league games because of the participation requirements for the LL All Star teams and tournaments. Those are the leagues that I see where the rec league tends to sustain itself in the younger age groups. But after 12U, I usually see them fall apart as well since the best players go to better TB teams, and the other girls lose interest.