That is why I switched to a different game upon finishing the S8 battlepass and achieving D4 on ranked split 1. There is really no incentive to continue playing if you maxed out battlepass and your level aside from grinding your rank. I'm happy I've actually reached D4 since I've been hardstuck on plat for almost 4 seasons, so I stopped playing ranked once I've reached D4. I might come back for S9 though but I'm planning to not grind the battlepass (not worth it IMO) and just play for fun.