You make it sound like everyone can just set aside at the very least $400 very quickly to build a low-mid range modern PC or buy a PS4. Not everyone has an income that would allow that (some are kids/teens, jobless, minimum wage and paying rent/utilities/food/etc). Yeah, they could stop playing the game and set aside the $12-15 per month on this game and buy/build a rig in a couple years with that money saved. But some would rather play on a system that's a bit underpowered for the game than not invest their time into it at all. SE is still supporting the console, until the system is dropped the players using the PS3 expect the game to run as close as feasibly possible to the PS4 and PC. The PS3 is still in their development support, everything needs to work as best as feasibly possible for all players in the game.
One must understand that a fix isn't as simple as just whipping up some code and everything becomes fine and dandy. A lot of meticulous tweaking has to be done in order to have it function in the most efficient and optimal way.
The amount of players in the area sends a lot of data to the system to render them all in the same place, added with the large Hunt mob, plus all the surrounding monsters potentially in the vicinity to the player is a lot to render.
Due to the miniscule amount of RAM (256 for the CPU and 256 for the GPU), the complexity of the cell processor (and different architecture to the Windows PC/PS4 versions same x86 architecture), SATA HDD port (SATA1, 150MB/s maximum), and the comparatively weak power of the GPU; the PS3 it can't render them all at once as they move to and fro. While it is trying to, it simply cannot keep up when so many things are in an area that need to be rendered.
Particularly because of the miserable amount of RAM in the PS3 and the way it's been allocated; the system has to load, dump, and reload assets far more and much slower than say the PS4 with it's 8GB of GDDR5 RAM. It also does it at a much slower rate than a modern PC can with 2-16GB of DDR2-3 for the CPU and 512MB-2GB of GDDR3-5 for the GPU. In a nutshell, the PS3 has good hardware from 2006.
Further adjusting the load priorities could somewhat alleviate this, but it would be like putting a band-aid on a wound several times bigger than it can cover. They could also try to further optimize the engine for the system (not just load priorities), but that would take quite a bit of resources and time from the devs when they're focused on making the content for all systems the game can be played on.
We know the PS3 is eventually going to be dropped, when is debatable.For everyone
Until it is, the PS3 will be the minimum spec for the game. And minimum spec needs to run. The players expect SE to do their damnedest to keep the game running on it. The system is underpowered for the game, nobody denies that, but all content is available on it and can be done on it. The hindering factors of the hardware can be worked around to a point, and SE has been doing their best to make it work on the system. Players will be playing FFXIV on the PS3 until support is dropped, and SE will be supporting the system until they decide it's time to drop it. Until that time, the devs are working tirelessly to prevent any player from being at a disadvantage in any content due to hardware restrictions. Should be commended for their efforts.
And I am a PS3 player. I can play on PC (played a bit of 1.0 when I got the CE, which ran at a steady 9FPS), but mine is not powerful enough to play the game well at minimum settings (15-20FPS depending on how many player models, effects, and environmental shadows are being rendered).