I don't see any serious issues with the linked question. It seems clear and includes some history of what you've looked into already. It's really no different than the numerous fastest way questions that are generally accepted.
As for speculations of why it might get downvoted, there's a few possibilities:
- The post reads a bit like you want to avoid putting in the work. Many games with microtransactions, paying real money is the "get rich quick" option. I'm not familiar with that particular game, but perhaps wording the question to ask which specific levels/modes offer the most currency per amount of playtime?
- Someone simply has issues with that particular game. Not a good reason for a downvote, but there's no requirement that reasoning be valid.