That's a slightly different topic from what I was talking about.
You're talking about a fairly wide variety of shows, often dubbed "Slice of Life", that don't really feature plots with dramatic arcs, that don't feature conflict or any of the stuff associated with traditional storytelling. As you say, how invested you can be in such works depends upon your attachment to the characters and setting and whether or not you're happy to just experience the mundanity of their lives without anything traditionally "interesting" happening.
What I'm talking about stories which are "about nothing" in a thematic level. In other words, they feature all the elements of a normal dramatic story (character development, conflict, etc) but lack any substance or message. They aren't interested in exploring any interesting ideas, they're vapid and empty. Eureka Seven is ostensibly a mecha action series with a strong relationship/romance element but it's also interested in discussion other topics namely humanities relationship with the environment, with each other, the consequences of violence, the nature of war etc etc. It may not explore all those ideas equally but they're all present within the text to a degree where you can easily identify them and recognise that the show is bringing something to the table, it actually wants to discuss important stuff. It's not just another mecha show where the chosen protagonist has to fight the bad guys in his sweet robot.
There's nothing wrong with simple, shallow shows. When they're done well I enjoy them immensely. But the problem with shows that attempt to very dense and full of ideas but are essentially completely empty from a thematic standpoint is that they aren't very interesting and it's hard to care about them. The case in point was AO, a series brimming with ideas and concepts and story but which was essentially a mess with nothing to support it.
