Well... You make a good point as to why they should build their communities here. The problem is that there is a tendency in the crypto sphere of people calling other projects shitcoins and trash.
You could build the best social media site on top of STEEM and Vergians, Bitcoin maximalists, Eth lovers still wouldnt use it... They would actually hate STEEM even more for it.
So really, projects building communities here is a stretch and wont happen any time soon.
Especially in a bear market when the competition is even bigger.
I hate to say it but hype is what will get folks here, not much else..