But that would mean Nintendo said no to those apps to the Switch, which would be weird, since that could bring bad press to the console ("Nintendo forbids companies from bringing services to the console" kind of bad press). Why would Nintendo say no to other companies developing sevices like those? Seems like nothing that Nintendo should bother about.
I don't know that they have said "no" to it. I just don't think they've actively pursued it. Hulu and YouTube are both available on Switch. I have a Hulu account, but I almost never use it on Switch since there is a Hulu button right on my TV remote. Accessing the app through an additional external is redundant and unnecessary. Same goes for Netflix, Amazon Prime, etc. With the proliferation of Smart TV's, there's less need for consoles to be used for these features. You shouldn't need your video game console to be running all the time if your aren't playing games on it.