Last I checked most cryptos have value.

They have value, because there are people who are willing to pay "real" currency for them. Although "real currency" is not the same as "real value", it just means that its recognised by law as a means of payment, inside a society and to its government.
But imagine, all cryptos could only be traded for other cryptos. No problem, since according to your statement, they mostly have value?
Far from it! It would become a pointless exercise to trade them, since you couldn't get anything "real" for them. The whole crypto market now is just a "search for the bigger fool", as Peter Schiff likes to put it. Just as the tulip mania was in the 17th century.