Pretty much with BC, there are two ways to go with end-game:
The PvE route where you spend hours looking for a group for instances or wait a week hoping 10 or 25 guild members get on to have the chance to win gear.
Or the PvP route where you can practically instantly get in a match and earn points to get gear.
Personally, if Blizz removes PvE attunments, there should be no restrictions on PvP.

It's possible that they're trying to do what you said. However, I doubt they're trying to scare people away from the PvP system into the PvE one. However, it should be noted with the ability to get Badges of Justice through daily quests, they made PvE a lot less exclusive.

It's my guess that they wanted to make PvP gear semi-exclusive to try and make a "progression" system for PvP.

The problem is that there is no end game for battlegrounds anymore. It isn't competitive at all. So, Blizzard can't make the battlegrounds gear exclusive via battleground performance. Especially since, to be fair, battleground performance at the PuG level is really only 1/10-1/15th your performance anyway.

I don't have a solution, I'm just pointing out why they're forced to do it this way.

Just a note, the released attunements on t4-t6. Now s1 and s2 are purchasble through honor.

I don't see that much of a difference there.