are you asking why english should be taught in non-english native countries, or in anglophone countries? Because the former should hopefully be obvious, being able to understand and use english is pretty useful these days…
The latter, teaching languages to people who already know them, is something i’m more iffy about.
I think it’s dumb to make it mandatory, instead we should have optional general linguistics courses and encourage people to read.
Maybe as part of history class you can learn about how your native language was spoken in the past, as well!