clearing new raid is no feat since it can be done in 6 people party - Legends dit it
We cleared that raid easy and were first time there, didn't know anything in advance. Assuming you watch out about basic things to not get one shot by mechanics it is very easy, certainly easier than fractal.
Now there is one more thing to consider.
You say it is easy so 6 people can do it. Yes, it is easy for teams who are high runed and well equipped with CS stuff.
But you must also consider that people who are very low CS and no runes, or very low ones will also try this once they reach 83k (specially if they additionally carry lower geared friends who don't yet have 83k). For them it will be tad more difficult and they will not do this in 6 people for sure. This is situation as it stands at the moment.
And those people also go to battlegrounds, in fact they constitute a large part of battleground community. So even if top guilds do the raid quickly and then can go back to BG. This doesn't mean most of player population will.
Therefore new raid IS one of the factors of BGs popping up slower.
Have a nice day.
not much time for bgs 
