You can of course consider the money you lost as the payment for the fun. Like going to play arcade games for example.
But trying to recover the lost money by gambling more is probably one of the worst things you can do while gambling. It's a downward spiral from there.
The problem is, the "fun" part of gambling is the expectation of winning. Sure, there are some other factors, such as drinks or social interactions in brick-and-mortar casinos, but I can't imagine many people would bother stepping into a casino (or logging in) if they knew
for sure that they will end up losing.
So gambling is not quite like other forms of entertainment and you can't really separate the "fun" part from the money.
And, what's funny, most people would probably feel much better if they drank away $200 in a bar with their mates, than if they lost $100 in a casino. Because losing always has some negative emotional load.
Adding to your point about the expectations of wins versus the fun factor.
To some people (specially who are very new in the world of gambling and betting) if they wanted fun, then they could easily buy some game or even find very good free-to-play ones in digital stores like Steam or Epic games.
You may never hear some newbie gambler to say "Ill go to the casino to have fun", they will likely always mention the possibility of big wins. The difference is the reaction to the losses and bad luck.
It is one of the reasons which leads me to believe that those who are not mentally prepared to assume losses are more prone to spiral down into problem gambling.