I can think of three reasons:
1) Many Americans are not wealthy enough to be able to subscribe to multiple streaming services.
2) Many Americans can't afford to pay for high-speed internet services
3) Many Americans don't have the family income to buy "a fucking gigantic HDTV. In my room we have another one. Every room in this house has an HDTV with streaming capability."
I understand where you're coming from but a trip to a cinema is arguably less affordable than streaming. If you can't afford a month's worth of Netflix and access a device to stream it on then a trip to the cinema would be a luxury well outside your limited means. The response of cinemas to dwindling demand has been to hike up prices, which I'm personally fine with since I'm happy to support cinemas for now. It does mean that the cinema experience is now less an accessible means of viewing movies and more a means of viewing movies as their creators intended them to be seen, at a premium.
That is the argument for cinemas now, I think. Regardless of the size of TVs, there is no way to accurately recreate the cinema experience in an ordinary home yet, either in terms of the audiovisual presentation or the communal aspect.