Why can’t foreign films make as much money as American films like Avengers Endgame can internationally?

The success of Endgame is due to several things. Consider that this is not just one movie, but the final, or at least latest, film in a 24 movie arc, which promises the happy, or happyish, resolution for the story that did not seem to be possible at the end of Infinity War.
Just the investment of making these films could ruin most foreign countries.
The biggest foreign (not American) franchise is probably the James Bond series, which has done well.

MARKETING!
The last avengers movie had a 400 million production budget.
It’s marketing budget alone was 200 million.
To put that in perspective, the most expensive non-colonial movie, Monster Hunt 2, had a production budget of a mere 140 million.
And I bet you have not even heard of it.

Hollywood blockbusters are created solely to make money, that isn’t so true of many foreign films. Playing safe, the big Hollywood producers just make the same film over and over again with the same big name stars. There is much more diversity in foreign films.

Because blockbusters are made to appeal to the lowest common denominator and most foreign film aren’t.

I agree with @ragingloli
It is Marketing ( advertising TV..almost non stop).
To advertise on TV is very expensive I heard 50 thousand or was it million dollars were required.
Not sure of exact amount but its way up there.
Here is a link it cost 200 million dollars to advertise Avengers Endgame!
https://observer.com/2019/04/avengers-endgame-budget-box-office-marvel-marketing-disney/

“Does Hollywood truly have mastery in making high-concept movies such as Titanic, Avatar and super-hero films? Could that be the main reason?”
Only if by “truly have mastery in making” you mean in making money.

They have the most investment, name recognition, strategic marketing skills (and developed relationships with theater chains, etc) at making money from such movies, and are almost the only ones investing that much in making and marketing those movies.

I wouldn’t leap from that to the words “truly have mastery in making”, because those words to me seem to be about making great films, and I’m not particularly impressed by what they’re making, especially not the writing and choreography, which seem to me to be pretty mediocre in many ways. The formulas they used are designed to make them money, not to make films that are good in other ways than box-office sales.