I started playing in 1984, I would play a double header (Baseball) on Sundays and race to my local park to play my sunday night EE league. In all my years I never played a tourney with a league team, with the exception of our once a year annual Incline Village trip with the Poppers (Poppers was a half tourney players who played A/Major down to D and half family members)
Don't want to contradict what I am saying, but Thursday nights at the Creeks in Nor Cal in the mid to the late 90s they actually had not only an Open league but also a C league. The Open league had A/B/C tourney teams that were more or less 75% of their tourney roster and the C league were all tourney teams.
Thursdays was for their team's practices, now Friday nights was drunkfest all star various league teams with throw together teams from various tourney teams
I'd day 95% or more of those 123 teams that played that C regional 25 years ago were solely tourney teams and some damn good ones to boot
Sierra Power, CT Boys, Dan Smith Plastering, Kuykendals/Cuervo (Who had an unknown Pitcher at the time on the hill with a broken leg, He now holds the record for most MVPs & All tourneys in the Majors and has i think 11 major rings), 1st & 3rd, Ken's Solar, Bullys, to name a few.
Now what I think you are speaking of is league ball in ASA, shoot I played in Cedar Rapids in 2003 for ASA D's and it seemed like half the Iowa teams were league teams entering the tourney. That changed in 04 in Oregon then I went to Nebraska in 05 for ASA C's and i'd say there were maybe 2 - 3 league teams of the 77 that entered.
Maybe it's a mid west ASA thing where a lot of league teams entered tourney.
In my close to 40 years in Cali i never saw it.