Citation, please? Because my memory goes back rather far;
3.05 - Seal Rock is introduced as a new Frontlines map, widely regarded as one of the better Frontlines maps too might I add, so much so that Yoshida has described the upcoming new map as a Seal Rock II.
4.0 - Saw a complete overhaul of PvP actions. Wont comment on the quality of such an adjustment, but it was there right at launch all the same.
4.05 - Season 5 of Feast kicked off, lasting until 4.15.
5.0 - While nothing on the level of 4.0s changes, we did once again see adjustment to PvP actions. Made their whole "We're not talking about PvP yet" during pre-release interviews a bit odd, given they did actually have changes to show us, just that they opted not to talk about them in the lead up to the expansion because... PvPers aren't worth it, I guess?
They clearly do bother with PvP at expansion launches. They do balance changes, and in the past, they delivered new maps and Feast seasons with far more expedience than they have with Shadowbringers. Shadowbringers, for some reason, has seen a shift in their approach to PvP. They're clearly still bothering, it's just their approach is... Muddled? I don't know, that's the best way I can describe it. I wish they weren't, as you put it, bothering with PvP right now, because then we'd still have 24 player Frontlines to enjoy. As it is, they're focusing purely on Frontlines, completely at the expense of Feast for some reason (I thought Feast and the FRC was SEs up and coming eSports (a joke in it's own right), why then throw it under the bus like this?), and then awkwardly deciding to just butcher Frontlines all the same. Imagine if they announced the new dungeons for Shadowbringers, then also announced that they're deleting the Duty Finder, that's the level of bewilderment I feel here. It's still possible to get into Frontlines, it's just now far harder and pops far rarer than it needs to be, because... Why exactly? As I said, I wish they were doing nothing with PvP right now. Nothing is better than being shot in the foot like this...
Like... I don't mind the new map being in 5.15, when Seal Rock was 3.05. A delay like that is completely understandable. Feast seasons simply not happening anymore? Less understandable, there's no real reason we couldn't have had at least one season already. Everything else? It's just a complete and utter nonsensical mess... I mean... Why were the 5.0 changes there to begin with? They were almost completely swept away by 5.1, and for the most part I think 5.0 was a solid improvement (some jobs of coursed needed some more attention, but I'm sure they could have gotten it if literally every job wasn't then changed), where as 5.1 is a disaster... It's like they showed us that 5.x PvP had some great potential with 5.0, then decided to just throw it all away with 5.1, to cripple Frontlines, not bother with Feast or Rival Wings... I just cannot get my head around what their development cycle must be like for any of this to have happened...