In the end i think you're complaining about the audio, but go argue with Apple not with me.
That has been requested for years now.
I think it isn't Apple where he should complaint but Google because YouTube is ofcourse from Google.
It seems odd that the official Google YouTube app still doesn't have an option to play in the background.
Luckely there are alternative YouTube apps e.g.
iMusic Fl - Free, with ads -
removed from the App Store
Tubify for SoundCloud - Free, with ads
Tubidy - Free, with ads (SoundCloud)
AudioTube - press box to cache/download > Menu > More > Video Cache, Free, 1,99 in-app purchase to remove banners. Can show video/audio offline (and choose quality), does play in the background -
removed from the App Store
Musify - Free, 4,99 in-app purchase to remove banners and have unlimited downloads. Can only play audio, no video. -
removed from the App Store
PlayTube Pro - first play to cache it -
removed from the App Store
SongFlip - removed from the App Store
These can continue playing in the background (and have offline listening and/or watching). For as long as Google didn't file a request to have them removed.
Other great non-YouTube offline music iOS apps are:
MusicSense | download offline track (one by one) for smartradio around a certain artist/track, unlimited skips, free app, no audio/video banners or ads. (not available in the US but in Europe only so it seems)
The Artist Union | download offline tracks/mixes
MixRadio - stopped their activities in February '16 unfortunately | 4 offline playlists (2+ hour per list) for smartradio e.g. genre, artist(s), 6 skips per hour, per playlist limitation, free app, no audio/video banners only small banner in bottom.
Soundflake for hearthis.at | Free, but offline feature is 2,99 dollar in-app purchase. Only get (mix) music from hearthis.at.
Hype Machine | 3,99 dollar, offers offline feature
CloudBeats | 4,99 dollar, offers offline feature for own music on cloud storage