Really?
Two fairly obvious reasons I can think of in ten seconds: sympathy for other people, and the desire to not see the entire sector tarred as a giant scam. I suspect there are other valid reasons.
Also, if these "experts" are wrong and crypto currencies continue to do well then they've actually harmed people instead of helped. Are they willing to take that responsibility?
A bunch of people are allocating large amounts of capital to shams when they could have been making productive use of it, this both gives rewards, social power, and encourages scammers/fraudsters, but also forgoes investment in otherwise productive activities that could benefit us all.
In addition, there are very real concerns about government involvement, as well as the social consequences when mom/pop/sister/brother/anyone we care about loses their money to such...
I could go on...