Bot detection is not that easy. Yoshi P said in an interview that they will not scan the computer of their playerbase for bot- or cheat-software. So they have not many opportunities to detect a bot. They can use heuristics but heuristics are not very reliable. They still will need some personal ressources to detect and ban them.

You can help SE when you report them. It could be more reliable than an approach based on heuristics.

Cheers