Money was invented as a medium for exchanging value:
you give me value, I give you money,
then you give someone money, and they give you value.

In this scheme, the person who ends up with more money is the one who has provided more value to others. Everything is clear and fair.

When we win money, we break this scheme. In the same way it is broken by theft, robbery, or taxes. If money is obtained for nothing, it loses its value.

It would be much better to play for something else. For example, for points.

Cryptocurrency actually fits this quite well too. Especially coins that are given away in airdrops, or those that are easy to mine. Or, really, any coin that only pretends to have value.

So overall, it seems quite logical to me that the most popular board on Bitcointalk right now is the "gambling" section. The most obvious use case for cryptocurrency, wouldn't you agree?