Vanilla is a product of Lussumo:
Documentation and Support.
Which brings up the question - why do people continue to support the serial format? They wouldn't support serial novels or serial movies. The sales don't usually support the serial model - maybe if a book has some star power or somehow becomes a buzz book, but most just languish on the shelves waiting for a second shot in the paperback format.
There's a difference in content and structure between Black Summer #4, a chapter in the single volume complete story Black Summer, and the fourth complete volume book in a series of complete volume books.
I think you're arguing for argument's sake, and deliberately missing the point.
Do you like the fact that in comics, a single-finite Graphic Novel story usually has to be published as a "mini-series" with each chapter of nearly equal length, possibly by artistic vision, but more probably by editorial/publishing demand?
Lucas didn't release his Star Wars movies by the scene or by the act.
Changing slant slightly into the more theoretical, there are things in favour of the single - one which hasn't been mentioned explicitly is Price. It is difficult to convince someone to throw down over ten quid for a trade they've taken a fancy too. It's a lot easier for a couple of quid.