Everyone else really hit the nail on why: if you're not getting paid to upload (or getting paid enough to make it worthwhile), you post whatever you can. With that said, I'm going to throw you all a different answer:
I prefer updates that have good pacing.
This can mean a couple of things: something new has happened in the story, we've closed a scene, we're starting a new scene that carries to the next update, we learn something new, etc.
All in all, I want the story to feel like it's moving.
You can argue 1-2 pages can't do that, but I will also argue an update with 14 pages can't do this as well. A lot of webcomics (especially featured webcomics) will have 60-70 panels an update...and the story is moving at a snail's pace. Meanwhile, someone else who knows how to pace can keep the plot moving with just 10-15 panels.
The amount of pages can't fix bad pacing.
So whenever someone is able to have good pacing and move through scenes, I don't care about the amount of pages. It could be 1 page -- has good pacing? Then I don't care.
Side note: Also remember genres can affect the amount of pages/panels. A comedy doesn't need 14 pages/70 panels. A horror might need more than 1 page/10 panels. Again -- another thing about pacing.