Remember this can o ly apply to those countries where cryptocurrency is tagged as not legal.
If the developers identities are known, then they can be sued with appropriate violations regardless of their nationalities or if the country is crypto friendly or not but cases like this would be likely prosecuted successfully if there is strong evidence and if the country where those criminals are residing have extradition treaties with the plaintiffs country.
If developers stay anon such cases won't be encountered. Another measure should be put in place.
That is why its never advisable to invest into ICO's or IEO's without verifying first the real identities of developers or proponents of the project because if the project turned out to be a scam then the investors can file fraud charges to them and will have a higher chance of getting back their investments.
The fact is the jail sentence is very low, they get released after time is up and after freedom they start enjoying the money they scammed off people, the right penalty should be all scammers that are caught must return every penny back to victims after jail terms, this will be a big lesson for the rest
Of course! A longer jail sentence should be given to these criminals if proven guilty aside from paying full and appropriate compensation to the aggrieved parties.