Valuable assets like bitcoin are not to be spent on activities that end in vain.
It's not the value that makes Bitcoin not a suitable cryptocurrency for gambling but it's the volatility.
Gambling with fiat currency whose value can change within a certain period most people avoid it, I can't agree with people who use bitcoin for gambling.
That's the point, Bitcoin is a volatile asset and its value can change anytime which makes it a bad choice for gambling. Just imagine, you are gambling using Bitcoin when its price is $30,000, and after a while when you have lost some money, you see that the price has moved to $32k, that's when you feel that you shouldn't have gambled with Bitcoins and you could have more value right now.
One more reason why one should use stablecoins when gambling is it makes it easier to keep a count of how much you've won or lost.