I understand completely. I wonder why the block reward is so small though, shouldn't it match mainnet, more or less.

This just means there are people mining something worthless. Or, mining not for profit, since one does not sell testnet coins.

It's much "cheaper" to just run the faucets every day to get more coins than you can mining with a single S9. That's so strange to me, but I wouldn't know, I don't hang around the testnet often. I have some on a Lightning wallet, but I also got those from a faucet. So I "test" them by buying starblocks or something like that.

Seriously, what could the rational be for the mining difficulty to be so high, or does it simply not cost some rich miner to unleash a few machines on the testnet ... maybe they are old equipment running on solar or something.