Net neutrality would be awesome . . . but what I'd like is for YT to decide if it's a platform or publisher. If you YT is a platform (like AT&T) then they wouldn't be liable for 3rd party content. Users would decide what they viewed.
Whether or not they are legally liable, they are beholden to their advertisers the same as any commercial broadcasters. They tried a subscription model (youtube red / premium), and it has failed badly.
Their content restrictions are based on their branding and commercial appeal.
How so? Until YT is labeled as a platform or publisher why would it matter?
Because the definition of "platform" you are using is not the typical definition in relation to technology. In terms of legally requiring them to provide access it's akin to calling them vital infrastructure. In technology terms for instance the entire Apple ecosphere is a "platform", and it's always been extremely heavily controlled in terms of both content and technology. "The walled garden".
In defining online video platforms relying on user generated content as vital infrastructure you are ignoring regulation of the actual infrastructure (the internet, PaaS, IaaS etc), in favour of simply regulating the most popular products operating on them.
Also if you applied those regulations to all online video platforms relying on user generated content rather than just the most popular ones, you would create an enormous barrier to entry. At the moment if you wanted to create a competitive online video hosting service for user generated content, you just need to determine your funding model (which usually involves targetting a niche which is currently under served) and you can deploy it on infrastructure such as Amazon S3 and Cloudfront with a pretty minimal expenditure. Requiring open user access and subjecting that access to bureaucratic regulation would destroy that low barrier to entry.
It's not just youtube or vimeo that would be effected either. For a while there "digital free speech" activists were hosting their videos on Pornhub (hardly any content restrictions right?), until Pornhub stamped them down for being incredibly unerotic and interrupting their "business model".