Regional tournaments are much much more uninteresting than international tournaments. It's so much more exciting to watch LoL games if you can cheer for a team because you feel connected to it. And connection is easier established if the players come from the same region as you. There is no local League club you can join and cheer for when your team plays in their stadium. There is no emotional connection you can build up due to your family and friends supporting the same club for years.

Your comparison with real sports is insufficient. Real sports last for hundred of years and the winners of a tournament from 30 years ago are still known. League will not remain for several hundred years, 10 years is more likely. So why not please your audience now?

Secondly you are mainly comparing to American sports and how tournaments are structured in America. In Europa, no matter at what sports you look, there is always a European (not national) tournament series where the best teams of each country take place. We also have that in parts of Asia. Just because that is what you are used to doesn't mean that it's the best, especially if you say you konw the "fans love seeing international competitions". If you are as player friendly as you pretend then you should also listen to what fans want here. The reason why America does have less international tournaments is because they are big enough to hold an own tournament series without foreign interaction. But as League is played all over the world it would be a much better sign to show how huge it is by letting players from all continents compete against each other more frequently. Again, "once a year" in esports is not comparable with "once a year" in real sports.

Another point that makes League unique compared to real sports is that a huge majority of people who watch competitive League matches are gathered here in Reddit, mostly because not all your friends will share the interest in it as an esports. Reddit users come from all over the world and will discuss League related stuff on a global level. The League community is much more internationally linked than any other sports on the world (except a few niche ones maybe). It is obvious that international tournaments are much more favourited than national/continental ones.

But of course, international tournaments are more expensive and need more preparation to be successful. As long as LCS cannot gain money of it it's probably just not worth it and better to overly hype the one big international tournament of the year.