I mined BURST for a while, another PoS coin. It's been around for 7 years, works great, and solves the PoW power problem. It's got a lot of functionality built in for the nodes, like messaging and marketplace functions.

And nobody cares. If I had to guess, I'd say the attractiveness of mining the PoW coins is that it's very expensive, but accordingly very rewarding.

When the coins are cheap and easy to secure as a node, people seem to not be as interested, which means the coin doesn't get used.

Chia, Sia, Filecoin all are trying to do similar, but have added in a "distributed Dropbox". There are some interesting challenges there, like quintuple redundancy and having your files stored across multiple nodes in shards for privacy. But in the end, they seem to suffer from the same issue as BURST: their feature set struggles to create popularity because they're not Bitcoin.