Yes, technically xb1 and ps4 can achieve 1080p (though usually no more than 30fps at that resolution).

What I'm saying is that since 2005, when 720p become standard for consoles (not even 1080p!), companies are financially struggling to make content designed for that resolution: hi-res textures, hi-poly models and motion capture (which means paying professional actors too). You see, increasing the resolution doesn't necessarily mean better graphic if you don't do content designed for it: you may have sharp images, but it will eventually make textures look blurry and models too blocky.

AAA companies struggled to handle even 720p content without increasing production costs (which means increasing financial risks) and loosing more and more money each year (look at EA). The situation has worsen since the new 1080p standard (just look at what's happening at Konami, trying to exit consoles' business to work on mobile). AAA videogames' production costs went from $3M in 2005 to $20M by now. If companies can't find a way to save money and reduce financial risks, they won't be able to support 4k content any time soon. But it's ok, because they're probably going to stick to 1080p in this console generation, while making (intentionally) crappy ports on pc.