It's quite simple really. It's because the original design intent for FFXIV jobs is a diverse spread of jobs that roughly do the same thing while playing completely differently with different minor advantages which could be mixed and matched to make different ideal compositions for different encounters.

But the human brain, especially the more casual human brain, eschews the ability to play every job and actually strategize through this flexible design in order to always play their favorite job.

Over the years this lead to the developers caving into the casual mindset, because the casual mindset is the majority of people.

It was made all the easier after the first time the hardcore community had proliferated a meta gaming 8 man party composition in mid-late Heavensward. Once this became a hot topic, there came the conflict between hardcores and casual players. The casual players won out, because they had more man-dollars vs. the hardcores. Likely always will.

The homogenization came gradually to us since the start of Stormblood, often packaged in a pleasing way. Bear in mind that the first time it happened was the worst, and people of all walks CHEERED LOUDLY for it. This was in the removal of Cross-class skills and Cross-class requirements to unlock and gird jobs. This brought role skills to the table, and the impact of them was downplayed at first, because they largely did the same thing as many of what were considered to be the, "Optimum" cross class skills for job function. Many were lifted wholesale, name and effect, from prior cross class skills.

This was the first blow of the smith's hammer that reshaped every job in every role into a standard format. All physical DPS would now have Second Wind. All tanks would now have Dark Dance(renamed to something I don't remember(Anticipation?). Parry +30%). All healers would have Shroud of Saints (Lucid Dreaming). All casters would have Mana Shift.

It didn't seem bad, because it let people go to endgame faster. It made sure everyone was raid ready on their chosen job just by leveling one job to max level. And some of the abilities got durations lengthened or cooldowns shortened, thus become more powerful versions of themselves. Some of the role skills were also new, and allowed for some exciting recovery options that weren't there prior (Example: BLM could go into Ice mode and then Mana Shift without much loss on their end, greatly supporting their healers).

But what people failed to realize, and still fail to realize, is that by homogenizing optional actions you could take, this removed the unique cross class spread that many jobs had prior to this. This lowered everyone's soloing potential, as well as any potential for fight specific optimizations with those, "non-optimal" choices. It also took cross class DPS actions from Healers and Tanks and even some DPS.

Then, because not every fight reflected well versus these role actions, and because SE decided that some of the role actions were confusing role responsibility, the role actions themselves were trimmed in SHB, and then again in EW.

This caused them to also evaluate job abilities on an individual level and grade them in a similar way. Everything unique that could cause a clear cut meta composition to pop up again like in late HW would get axed, nerfed, or significantly altered every time one came to play.

The worst thing about it being that the math for each job was still different, and due to the original nature of the game's design, still led players to still find the meta comps. So the solution then became to make fight design worse so that jobs brought mattered less. Or at least, mattered less in specifically a, "Specific Job X sucks for this entire tier and should never be brought." kind of way.

In that they succeeded. And again people cheered it on.

We're never going to get them to make the game fun in the ways it used to be ever again. They are chasing dollars from the easy going people who don't care how complex or fun a game could be. These are their ideal customers.

And we have to remember, if they do some how return the game's form, it will just be a return to what we had before, not an earnest effort or innovative idea driving them. This would be easy for them to do, so it's more or less a win for them no matter what the demands of them become.

If some miracle happened, and the majority of people wanted a return to complexity, they can fall back on what's already there but unavailable currently, in other words.