Cryptocurrencies are starting to feel like that, a massive game that people take pleasure in. Nothing wrong with that. I've enjoyed real-world role-playing games, so I don't want to judge anyone else who is into such things.
Is it crazy to make a game currency your main form of investment? Maybe, but not automatically. You should, of course, invest in a diversified portfolio, but if you want to go long on this particular kind of game, it might pay off huge in the end.
I recall when I was a child me and my friends played Dungeons and Dragons -- long running campaigns that went on for years. One of the parents of my friends was upset by this and said it wasn't really a game because it didn't end and nobody could be declared a winner. I'm afraid my initial reaction to cryptocurrencies was similar, not seeing it as a game and rejecting it as not being real.
Of course, a big difference is that we insisted Dungeons and Dragons was a game, whereas the proponents of cryptocurrencies continue to insist that this is not a game. Some make some variation of the argument "there is so much money in this, it's too big to be a game" but that's an incorrect understanding of a game. There is a lot of money in esports, but we are still talking about games.
I've come round to accepting that cryptocurrencies are here to stay. I no longer consider them Ponzi schemes, I do regard them as a kind of play activity, one that deliberately tries to blue the line between play and non-play. To the extent that they enable certain kinds of criminal activity, they become real and can be used in non-play contexts. But mostly, this is a kind of play that some people find pleasure in, and there is no point in berating them for it.