U of M Learn or Third Party Websites?

So as many students might know, we have to pay extra for third party websites like Macmillan, McGraw Hill, Pearsons etc for assignments and quizzes. Question is what is the purpose of these websites? Like we already pay the tuition fees at once only to then discover we gotta pay another 60 or 100+ dollars for the websites. Forget money for few, what abt making it more complicated? Like why can’t you just upload that into the U of M Learn? Why can’t they keep it all in one place rather than moving it here and there?