Why does specifically Apple has to respond to this and not any other TV providers?
That's a huge drawback for Apple's offering, because a whole lot of people want to watch that stuff. If they want to keep their product relevant, they have to address it - but they now have a huge new problem in that every Apple TV has a YouTube app, and so do a lot of competitors in the space. They could've had first mover advantage on this, because up to now no one has managed it - but now it seems YouTube has, which leaves them playing catch-up.
Apple doesn't give out Apple TVs for free. The beauty of owning the hardware and platform like Apple does is that they still make money from other peoples services.
Now, whether they have a compelling enough TV hardware + OS/software for people to buy and watch Youtube TV over... that's another question. But I think that question exists regardless of whether Apple makes a linear broadcast TV streaming service or not.
The "reports" earlier, when Twitter was bidding for NFL (or NRL? I'm not American or into sport) Apple considered a bid but ultimately decided not to because they realised that whoever got the rights would just still stream it on Apple TV regardless.
I definitely acknowledge that Apple TV at the moment is Apple's compromise of not being able to put a better service out there, but I still think they're very happy selling people their hardware for other people To make software services over the top.