Because the guy had a Patreon charging for the mod. He was profiting from their IP, there are pokemon mods for hundreds of games and hundreds of fan made pokemon games that exist because they don’t charge for them.
You know how in default when you are in a battle and knock out an opponent’s pokemon, it tells you what they’re going to put out next and asks you if you’d like to switch pokemon? That’s ‘switch’ mode, in ‘set’ mode you aren’t asked that and have to use a turn to switch pokemon if you’re at a type disadvantage, meaning they get a turn of damage or set up. Really makes you think about strategy a lot more, and is integral to challenge runs like nuzlockes.
You think Ubisoft games will have modding? Hahahaha no, no it will flop on launch and the live service elements will die within a year