The other question you should be asking is why altcoin mining is not as popular as Bitcoin mining, especially after ETH stopped POW in favour of POS. For example why are we not hearing people buzz about Ethereum Classic, Litecoin, ETHW, etc.?
The answer is pretty simple... the profits are not that exciting. So same logic can apply to solo miners
Ethereum Classic and ETHW are dying coins. Even if you find a few blocks solo on these coins, the profit will be so minimal that you won't have much to celebrate.
I don't think a miner will solo mine Ethereum Classic to get a $30 reward, and the reward for ETHW is very small.