They have no third-party clients either, which I assume is to prevent piracy (which will happen anyway). For me, it has the opposite effect – I would pay if they enabled downloads. Now I just freeload the non-exclusive content off YouTube.
...Because I’m bad at identifying sarcasm, this section exists in case “Ain’t that a basic feature nowadays :/” was meant sarcastically (it could be because of how much more popular streaming has become as opposed to downloading). Well, I don’t really have mobile data (way too expensive in my country), so I pre-download videos to watch/listen to in public transit.