Investment and gambling is different, also the word "gamble" is a very broad word to begin with. I guess the right term to use when you're using your money in an investment is "risking" and not "gambling" your money because you put it in a game to earn money.
The other way to determine the difference between NFT games and gambling is that NFT games assures you to earn money once you started while in gambling, it is the complete opposite.
nft games give us the opportunity to get rewards in diamonds as long as we all play the game as determined by the developer.
indeed for now NFT is becoming a pretty good hype because apart from this it is an easy thing to solve.
different from gambling where this is testing your luck here and the chances are there are only two when you are in gambling namely the first you will win and the second you will lose