It's easier for everyone if BLU stays a tier behind. Why go through the trouble of banning BLU from savage (and EX) when they could just keep it a tier behind? Gearing up is easiest when they're a tier behind. Anyone that wants to play it next cap raise is already prepared.

The restrictions exist because they've taken the time to work on ~20 other jobs and something as OP as BLU needs to stay limited, otherwise you just have most everyone running around as BLU (which is actually quite the nightmare many don't really know what they're doing). There's tuning that needs to happen before the cap gets raised.