Putting a mechanic into your game where you spend real world money to gamble for skins and stuff. Game companies realized they can make a lot of money selling what modders used to be able to do for free. It's apparently a well known thing that there exist "whales" that spend huge amounts of money on these things. Probably a decent number are addicts being abused.
'gacha' refers to 'gachapon' in japanese, originally referring to lottery elements in mobile games (typically asian), now referring to exploitive microtransactions and addictive elements in all forms of gaming. Loot boxes are a common gacha element. The poster is implying that GTAV is exploitive.
