I think a few of us here won't want to hear it, but in my opinion the simple reason you like webcomic dialogue less is because it's worse.
Most webcomics we find are made by amateurs writing for the first time, whereas most manga have proven themselves by first being published, and then by being popular enough to be translated into English. I absolutely feel the same way as you, where I can easily sit down and read a novel or wordy manga, but when a webcomic writer drones on and on I think, "get to the point already!"
There are a few gems out there in the webcomic world, though, where the authors write paragraphs and paragraphs and yet manage to keep the audience engaged. You just have to look a little bit harder for them.
Here are my favorite wordy webcomics, if anyone wants reccomendations:
The Property of Hate
The dialogue helps to convey the whimsy and mystery of the world. There's a ton of subtext and subtle little references and puns that really show how much effort the author puts in. Also has some of the most incredible art I've ever seen in webcomics.
El Goonish Shive
Starts off very rough, but slowly evolves into a character-driven drama with well thought out characters who's inner lives are often conveyed through paragraphs of text. But I read every word because the author makes me care about these characters.
Doe of Deadwood
The dialogue is what kept me actually reading this one, as the quality of the art belies the quality of the writing. The characters' personalities come out through their voices, and that keeps the writing from feeling like lifeless exposition.