I'm over here in the fashion community just shrugging at the whole mess (we raid! we RP! we do all the things! we don't judge!)

But the real reason is this: The iron triangle, or the scarcity of resources from the development team. (The iron triangle in project management is time, money, scope.)

Raiders believe that SE should hire additional battle content programmers and focus their efforts on high difficulty, high reward content like the Ultimates, or hiring network engineers to fix the netcode to get ride of the deadly snapshots and server ticks that are the bane of their existence.

The RPers believe SE should instead hire additional infrastructure programmers, and work on stuff like making additional housing districts, optimizing the netcode to allow for more inventory, making a better glam system, male viera, hats, etc.

Every time new content is made for one group, they believe that those resources (money, time, energy, developers) is being taken away from the other group. And that is, in fact, true to some extent. Battle Director Gondai said during one of his Fanfest interviews that they made a decision to stick with a smaller number of high quality in house programmers, instead of farming out projects to subcontractors. The same is probably true for the zone design, the item design, etc. So resources for zones and characters and monsters cannot simultaneously be used for other characters and zones.