1) Wii U had a ton of apps, not just streaming but also things like Miiverse. Wii U failed and I think Nintendo's analysis of why it failed lead them to think a device more focused on just gaming would work better. The Switch selling as well as it has only supports their perspective on this, I assume.
2) Probably most, maybe even a super majority of people now have either smart tvs or use Chromecast sticks/fire sticks/Roku sticks. The software on Switch would mostly be redundant unless you are watching somewhere else, which many don't do (I can't see many Switch users whipping out the device to watch a show at a coffee shop).