It's all about utility. There are so many coins on the market, but only a few provide real use cases to the world. HDD-mineable coins are no different. I've never heard about MASS until you've mentioned it now. I'm going to have to do a little research on it to see if it's worth it. Still, no other coin compares with Chia as it's the most profitable HDD coin to mine right now (if I'm not mistaken). Some would say HDD-mineable coins are more decentralized than ASIC-mineable coins, but that depends on how the network is structured.

I think HDD mining could pose a higher risk of centralization as data centers usually have a large number of HDDs at their disposal. Imagine if Google, or even Amazon takes control of an HDD-mineable coin with their huge storage space. It would've been a complete disaster. I don't think they will be able to manage to acquire large numbers of ASICs, as such devices are usually more expensive than ordinary HDDs. The industry is just starting to blossom, so I'm hopeful developers would come up with a solution to make HDD mining more decentralized. That is if the hype goes back up again.