I forgot to explain why they can't just leave it alone and just continue milking whales their subscription/coin purchases: every 3-4 weeks they change the courses with new "events" and SURPRISE! Your expensive gear now here is useless. You grinded for days and/or spent $1000s to have level 8 "beach costume Luigi" that requires to literally find ONE HUNDRED duplicates in the loot boxes? Sorry, those new courses unlock the max points multiplier only with the new "Pizza baking Luigi costume", go back to level 0 and climb the ladder again with the loot boxes, thanks for playing. Ah and the "Pizza baking Luigi costume" is a limited event, please find all the 100 duplicates in the loot boxes before the end of this month, or you will be never be able to level it again, thanks.

So Nintendo needs to pay a couple employees to think and create the new monthly events with all the new gear, takes a lot of effort, that's why they can't just abandon it and continue to just rake in the money from whales