Because it's a good excuse. No paladins will deny that we are one the top healer now, but not because of our healing. I mean, not entirely.
We can top people with our new "NS" spell buffed in 6.1, and with wings. This spell heal for 60k to 200k (Used alone to used with wings+both trinket if you are human). Outside of that, a shaman (any spec) have more healing than us.
But it's "fine". Why? Because the current meta game allow paladin to shine only with wings, and of course saved by the light, a good (but ridiculous) spell which allow you to save time before the CD of wings or sentence, when your CD rotation can begin again. Sacrifice is 90% used to prevent cc (Not to reduce damage), BoP is 100% used to REMOVE a cc, not prevent damage. (Considering purge).
It's like the season 5 in my opinion, paladin are really good, even the top healer, but for wrong reasons. We've always been a comp-dependant healer, and i don't remember a season (outside of season 5 perhaps) where someone said "add a hpal in your team, and it's viable." We can say that to shaman and druids for example.
Ask any paladin, everyone tried to play without saved by the light in 3v3, it was a disaster (Other talent are either bugued, either more PvE/RBG oriented). Add a constant pressure team against you (WLS WWLS), and you will struggle to heal until your CD are back. (Saved by the light, Wings, ES).
I think every paladin would want to remove this overly dependance on wings / saved by the light to be viable.