I watched the news that ransomware which spread in the network virus Petya earned only a little more than 10 thousand dollars. It seems to me that if this is the case, it is possible that they create such a virus spent more than earned. Maybe they have no more desire to spread these viruses?
I doubt that whoever is creating ransomwares is trying to accumulate wealth. If someone have this knowledge to build such a powerful tool, he shouldn't have any issues finding a job. It's probably some people trying to send a message (whatever it is), the amount they got is from people who paid, however, the losses could be in millions for the companies that got infected since they can't access their files. Hackers tend to have a different mind set then other people for some reasons, money is not their priority usually.