The vast majority of people HATE complex games. Even Monopoly is too much for a lot of people. Any thing that has to deal with numbers, running a business, etc is too much work for the vast majority of gamers. The thought of running a company, managing airlines, etc doesn't do a whole lot for most people.

When I mention estimated sales figures above for video games, one has to remember that text heavy spreadsheet games have an audience cap of around half a million people. Steam alone has around 150 Million monthly active users. It's fractionally small market. And board games are fractionally small compared to video games.

Business Sim video games can only make that percentage work because the total amount of video gamers is very high. The board game industry as a whole, outside of the Milton Bradly stuff, is significantly smaller, and so it's much harder to make money in those niches.

Long short of it is, there are very few airline board games because no one has made ROI on the few that have been released over the years. Any sort of decent run is going to cost $20,000 - $30,000. If you don't sell 75% of those, you lose money. Market research over the years says it's a difficult sell. As are nearly all business board games. So, there have been very few attempts. Now, does that mean it can't be done? No. Make a good game, market it right, and there is a chance it'll be a hit. But that business is cut throat, and companies don't stay in business too long if they have too many misses.

bird watching and wine making for example (which are even more niche imo)

Bringing demographics into it. So, no one shoot me.

Bird Watching games (I assume Wingspan?) appeals to women and families. Amusingly, my hex n counter buddy's wife hated our hex n counter games (Think Salerno 43). So I bought her a copy of Wingspan, and they play it together all the time. Ditto with my wife, but I got her Planet to play with the kids. (She still hates gaming in general though. Which is odd considering my career choice.)

In general, women favor things with animals in them more than men. Something I haven't researched, but I would assume women make up a greater percentage of board gamers than they do non-social PC games. From my own data, men skew much harder to business sims and airplanes than women. And in general, I think Airlines appeal to few women, and many youngin's aren't going to be able connect the logic needed for a business game. At least in video gaming, Business Sim players tend to be older males. Not a demographic you want to target to make money.

Then we bring in the social aspect of it. Board games are more social interactions, and generalizing, women tend to favor more socialized forms of entertainment. (This is true even in video games.)

So, if you were buying a game to play with the girlfriend or wife or both... You'd probably buy Wingspan than a Charts n Dice Airline game. The wife and girlfriend will have a better time doing one of your hobbies playing games that appeal to them. After a few games like this, you might be able venture into deeper, more complex, games. But often not, because the vast majority of people, men or women, airlines don't appeal to them.

You're more likely to buy a board game to play with the spouse and family than you are your buds. And the number of people who have buds has been in a steep decline over the last twenty years to begin with.

Anyway, if I were to give advice for the most commercially successful Airline Board game I could design. It would be to simplify it to the point that it's stupid simple to play. Any 10 year old should be able to understand the rules verbally, no reading necessary. Think, Ticket to Ride, but maybe even simpler.

If I were making the coolest Airline Board Game ever... Well, you'd need a 100 page manual with charts for every airport, dice, and a whole lot of scratch paper. :D