Is solitaire fun?
Really an impossible question. It's like 'why do people drink beer?' I mean, I know of plenty that don't like the taste. But I like it.
Why do they still sell board games? I mean, opponents for board games, they are rare and that's been the truth since 1970. But they still sell.
There is simply nothing wrong with playing a side, making the best possible moves you can reason out, then putting the other side's hat on and doing the exact same thing again.
It comes down to, do you like the subject matter enough to want to examine it while simulating it. I can't for instance enjoy WW3 concept games. But I have emotional baggage called Cold War syndrome. I didn't think the 60s and the 70s were very fun. Thus, I have no real interest in games of that subject matter, so it's not relevant to me personally if Flashpoint is any good.
But I like examining the time period through board games. They also help visualize the scope of the event. They allow you to ponder, what would have happened, if they had pursued this course of action? Good games permit a decent window.
Sometimes a game is just a game, and sometimes a game is just an interesting interactive tool.
I will likely never have the chance to play this against a living breathing adversary. But I likely will greatly enjoy playing it.
Everyone approaches 'fun' in their own way.
I have too many too complicated wargames, and not enough sufficiently interested non wargamer friends.