How is this an ad? They are informing you that you can get more out of your subscription. Would it be better that they’re didn’t inform you about this and hid it away in some obscure menu somewhere?
There are lots of reasons to not like Google/YouTube, but I can’t see how this is one of them.
Edit: There is also a clearly visible dismiss button.
Isn’t it also partly that as processing power increased, you could do more sophisticated compression/decompression in real time compared to previously, allowing these more complex compression algorithms to actually be viable?
I.e. they actually knew how to do it before, they just didn’t have the power to implement it