Some schools do. My boys are at a bilingual school. 2.5 days a week they are taught in their second language. They do maths, literacy, PE, arts etc in that language. Their teachers are either native or have very high level fluency because the school's expectation is that excluding situations where a student is at risk that the teacher only communicates in the second language. DS1 had no idea that his kindy teacher could speak English until the last week when he busted her talking to me in English.
I am unfailingly grateful that I can access an education like this via our public education system and I wish that other students could have the same access.

But even a few hours a week is better than no language options.
If only we had enough bilingual teachers to do this! It's such a good way. And I agree with the the couple hours being better than nothing. When adults want to learn a language we get far less time than that!