This is more an issue of economics than anything else – as the cost of production, printing, and distribution of paper comic books continues to rise, it's harder and harder to profit from a "B-tier serial", or to expand the audience for any comic outside of hardcore fandom (though it does happen).
"Self-contained stories", or at least "digestible compilations" such as graphic novels of serializations, however, have taken off in the last decade for a few simple reasons:
- economies of scale allow for a much cheaper $/page ratio for the reader ($3/32 pp for comics vs. $10/200 pp for GNs)
- the larger format GNs look a LOT like "regular paperback books", which is a product that all kinds of retailers, not just bookstores, already know how to shelve and sell.
- Comics, on the other hand, typically require specifically constructed wall displays, or space-inefficient and clumsily-operated spinner racks… They are smaller and more fragile than other magazines, and while their content should be more evergreen (a big problem with selling older/out of date print mags like Time, say), there are so damn MANY of them, it's just too hard to keep track of inventory/stage them nicely/etc.
- For non-serialized single volume work of appropriate length (150-300 pp), it's also now possible to make a profit with the more friendly book/box store/discounter/toy and game channels to exploit on top of the dedicated comic book market.
Simply put, it's easier to display, sell, and manage inventory of graphic novels/longer form comics, and theoretically no less so for a single volume work (especially at book retailers – keeping all 42 volumes ofin stock at a given Barnes location, for example, is a complete NIGHTMARE).
But, you say, this has not answered the question "do people still WANT to read…", and you're right: what people want is not the same as what the publishers want, which also differs from what the retailers want. It's a game of finding equilibrium between all three, and a messy game at that. Perhaps I could simplify it further: what people want in comics, and how much they are willing to pay for that stated want, are often out of alignment.
This is one of the reasons why digital and online publishing hold so much promise (outside of, er, monetization) – they are FAR more closely linked between creator and reader, with fewer middlemen taking a cut, or enforcing limitations over content or frequency.
Do people want daily/weekly/monthly "chunkable" serials? YES. Do they want nice, tightly wrapped stories/arcs, even if that means a year between releases? YES. Are you more likely to find the latter at Target, or even Amazon.com? Most certainly!