I hypothesize three reasons for this:
(1) The skills behind hype often do not intersect with the skills behind actually building great stuff, or at least rarely do in the same individual.
(2) Every individual and team only has so much time. You either spend that time building stuff or spend that type hyping. If you spend that time hyping you're not building. If you spend your time building there's no hype because you're not out hustling and blowing hot air.
(3) More knowledgeable people are skeptical of hype and tend not to spread it even for things that deserve it. Less knowledgeable people are more likely to both believe hype and spread it. Hype for things that wow the ignorant has better virality than hype for things that wow the knowledgeable since even when 'wowed' the knowledgeable tend not to spread hype.
Even in cases where there's a lot of hype around someone or something with substance (e.g. Elon's ventures) hype still tends to far outrun substance. I just take all Elon's time estimates and multiply them by 2-4 and I discount the more extreme stuff as likely just hype. "Oh that's cool, I'll believe it when I see it." But Elon's companies do actually deliver cool stuff and I try to judge them objectively on that as if the hype didn't exist.
It's really bad in the cryptocurrency world. Below the top two or three many of the highest market cap coins and other crypto systems are half-baked things that don't work, mere clones of Bitcoin that have been heavily pumped, or even outright scams. Stuff that works and is novel is relegated to pages two and onward on coinmarketcap. Case in point: Filecoin raised massive amounts of money on nothing but a white paper while Sia had a working system (though still not good enough to displace Backblaze or S3) and raised a tiny fraction of this and got nowhere near the hype.
Edit: Considering all of the above I consider hype a contrarian indicator. Without a whole lot of substance just under the fold (e.g. SpaceX) it's a powerful contrarian indicator.