The remaining 2 of the 3 founders left 2012 or 2013, after ME3. No idea how much the other staff changed, but I suspect that was the tipping point.

Every time a competent and passionate gamedev leaves a AAA game studio, a new indie studio is made.

Unless of course they can't afford to start a new indie studio and have to pick up a trade that actually pays the bills. Gamedev is the worst part of the software industry to work in sadly.