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The advantage of bitcoin is even if the market collapsed still we cannot be consider at loss since as you said people can do something like just hold their bitcoins and wait for perfect time for market to recover. Unlike on gambling if we lose we can't recover it back unless we continue to bet and will be in more bad shape if we are not lucky then we encounter a losing streak on our bets.
Also for popularity discussion gambling is first known before bitcoin and its just casino owner just adopt the market of crypto and they use this as payment methods for crypto users to play on their platform.
And when we lose playing gambling using bitcoin, it is clear that we suffer losses because we lose some bitcoins, which are not easy for us to recover from. And this is why people have to change their minds about not using their bitcoins too often and choose to use altcoins for gambling. Besides having low transaction fees, altcoin prices are also not very high compared to bitcoin prices. And when gambling, the minimum bet for using altcoins is different so they can avoid big losses. But when they experience defeat in using bitcoin, it will hurt. But for now, bitcoin is better known and popular because people already know the uses of bitcoin other than gambling, so some of them use bitcoin as an investment instead of using it for gambling.