Because then Google (YouTube) would force the competing app off the Google (Android) App Store for not meeting Google's (YouTube) own censorship policies.
It's literally their written policy and has been enforced multiple times. App store and GPlay apps have to adhere to Apple/Google set content standards. You can't host 'free speech' apps there because trolls instantaneously fill the 'free speech' apps up with visibly anti-semitic content then report it to google and down it goes.