Dual DA/ECNL Clubs were given an "all-in ECNL" option from ECNL this off-season. If they went "all-in" they were given the option of having two ECNL teams (to help the transition of moving their DA players to ECNL). Imagine the pissed off Slammers families, if Slammers went back to ECNL and had only one team. Many of the current players on their ECNL/DA teams would be cut from their now only one ECNL team. So ECNL gave these dual clubs an easy transition. This is why Slammers has two teams. I do not know if they will keep it permanently or just until these age groups age out.
If these dual DA/ECNL clubs did not meet a very high competitive bar, they were told by ECNL that you are "all-in ECNL" or you are out. West Coast (OC Surf) was one such club that did not meet that criteria. So they chose DA (a choice they probably regret since so many top clubs -Slammers, Michigan Hawks, Elipse, PDA, etc - all publicly dropped DA after OC Surf chose DA). Slammers obviously met the competitive standard but still chose to go "all-in ECNL". Blues met the competitive standard too. So they can remain a dual club.
It appears to me (but I do not know for a fact), that Surf was given the take "all-in ECNL" or you are out ultimatum. They were probably campaigning to stay in both, but ECNL is firm on their competitive standards. Surf probably lost their argument to be an exception, and is now caught holding the bag with their families.