Say you take 10 grand to Bob's Casino in Las Vegas, buy chips and turn them into 100 grand at blackjack. You put the chips in your bag and go home to sleep because you're pretty drunk. Bob's Casino burns down overnight and Bob announces it he now bankrupt and going out of business. Your 100 grand in chips are now worthless.
The top answer for "are casino chips legal tender?" on Google is Because casino chips are not legal tender, they are not legally transferable. That doesn't mean some people don't try to exchange them for cash or chips at rival casinos. Although the practice was once popular in Las Vegas, the government stepped in to prevent money laundering and counterfeiting.
The U.S. dollar is the global reserve currency because it is backed by the full faith and credit of the U.S. Government and people have confidence the U.S. will last. Bob's Casino chips are back by Bob.
NFT's are backed by who?