It's not just miners, you also have people using your free or even cheap tiers for DDOS/PortScan/SSH Bruteforce. These ones burn your IP address so it's better to prevent it than to try to catch it later. A credit card check goes a long way as a barrier to entry.
As long as it is free miners will keep trying to get around it by for instance running tons of different free accounts each with a obfuscated mining system.
Even if you catch all just having them try will be a huge waste of resources.
Sure ... look for high CPU then anonymous miners cap their CPU usage. And a few legitimate users (and potential customers) get locked for reasons they don't understand.
Repeat with every other trick you use to detect abuse.