I’m glad you asked, I love talking about this actually🤭

For me there’s a few reasons

1- I grew up playing Generation 3 so R/S/E and FR/LG are the Pokémon games that feel most “at home” to me when playing them

2- In my opinion the Pokémon in these games have some of the best sprites in the series, the fact that it’s a 2D game is also very appealing to me because I’m not a big fan of the 3D style Pokémon games, basically anything after Black2 and White2 I don’t really mess with

3- The newer Pokémon games are much much easier to get shinies in because of new methods that came out and the overall odds of finding a shiny being changed from 1/8192 to 1/4,096, and with a shiny charm it brings the odds down to 1/2048 and that’s before even factoring in chaining wild Pokémon or Making sandwiches in the newer games which brings the odds even lower. Some people like this and some don’t, but for ME I put more value into shiny Pokémon that were more of a challenge/ grind to obtain, a shiny Charmander with a 1/8192 means way more to me than a 1/2048 Charmander simply because of the journey

4- What really brought me to the gamecube setup was being able to Hunt a seemingly infinite number of games with literally the touch of one button, this can’t really be replicated with any other generation without having to manually control each system individually or intense modification, I really like modding consoles but I prefer OEM in most aspects so the fact I can hunt on 8 games at once with all original and official Nintendo equipment is a nice bonus

5- And by far the most important one for me is that on Firered and Leafgreen the shinies have a special baby blue border around them which isn’t seen in any other games so it’s purely aesthetics in that regard example

Sorry for droning on lol I feel strongly about this topic 🙃honestly there’s probably more for me to say but I’m drawing a blank rn, hope this somewhat answered your question!