so why Cryptos if they do not build a new world but just become some "assets" for (fiat) speculations ?

One reason I could think of is exactly community-driven websites like Hive. You can't have that system based on Fiat because of so many bottlenecks that are unsolvable in tradfi and the legal system around it.

I would also say that it is too early to judge if crypto will replace fiat or not. It can certainly be complementary during the transitory period but it's not that easy to value things in crypto or BTC when we can't really determine the real value behind it. As long as the speculation game is played very little will change in that sense.

But, again, crypto has already changed a lot of things in the world. Earning potential online has gone through the roof. Seems to me anyone can earn money working in this industry as long as they want to commit and treat it as they would a "real job".

That is a big step forward imo