As seen by many sandbox MMOs, or games like BDO and upcoming AoC...producing content for PvPers is vastly easier and takes far less work and content for them than it does for PvErs. For example, if BDO removed PvP...what would be left? Grinding and some crafting stuff, but otherwise really limited content. Hence they know despite so many requesting PvE servers for BDO, that they'd then need to actually spend money and resources to make PvE content. When PvPers are much easier to keep happy...throw them in a battleground to fight over a keep or castle or some part of land and that is good enough for them.
With how negative BFA has been...the vast majority of negativity comes from...guess who? PvErs (not all, but most).
PvPers overall (not all of course) but mostly are enjoying warmode as their favorite feature in BFA. Warmode of course took little work for blizzard to make...pvp anywhere with it turn on/off. Even less work than BDO spent to make pvp content, since you can't conquer towns or land or anything in WoW.
I see the vast majority of negativity comes from PvErs, where as PvPers in general are happy especially with warmode.
Which brings to topic title...
Blizzard chose horde vs alliance as a focus for pvp conflict. Many PvErs pre-release were already unhappy with this choice, with reasons such as "wow a repeat of horde vs alliance rehashed, fighting the legion was way more epic". Where as pvpers pre-release were super excited. But, there is a reason companies choose pvp focused MMOs/expansions
It really takes less work, time and money to spend on PvPers than it does for PVErs.
of course one exception to the rule is EVE Online...it started off VERY pvp centric (and still is), except it was pretty barebones and pve was nonexistent pretty much. It took time, updates and patches and a lot of money and it can easily be played as a pve MMO with pvp active. A big reason its a successful MMO because it makes most people happy, except those who truly hate anything PvP.
Other than EVE though...most PvP MMOs are so lackluster on content, and pvp games in general...that the developers know they can spend little on content and features because pvp is free content that the developers don't need to spend any money on.
Which explains why the theme of BFA was chosen. Especially when in-game, a lot of it seems VERY forced and not...hmmm...not fluid at all. Not natural one bit. Like they really forced so many parts of the story to be PvP centric, instead of it making it feel natural it really does feel forced and like the whole theme was changed halfway through. Like blizzard had to meet a 2 year deadline and ran out of time to make PvE content, and the PvE content they had they had to rush out to release. So they had to forcefully change the expansion to be PvP based.
Which of course makes a lot of PvErs unhappy..but mostly PvPers like it cause it gives PvPers something to do and its much easier (and so much cheaper) for blizzard and every other company to cater to PvPers than it is for PvErs.