
Not sure, but it's probably because of the really unique storylines compared to the typical Japanese yaoi mangas. Well, that's what it is for me, at least. These webcomics lately are really hitting the whole interesting aspect nowadays.
No overused cliches. Deep characters. I mean look at Killing, Stalking. Like holy hell.

The easiest way to find out is just *READ*
http://www.mangago.zone/home/mangalist/106534/

A lot of people haven't seen them before so they think it's cool and exciting. Really nothing new though.

Maybe because they are so easy to read on your smartphone, iphone ....I've never read them until I bought myself a decent phone.

I find webcomics incredibly refreshing. I've read a bunch of Japanese manga and find a lot of them very cliché and forgettable. Although there are plenty of unique and beautiful manga, they are hard to find. Of course this is partially due to the large amount of translated manga vs the smaller amount of translated webcomics. Right now, webcomics seem "better" because only the interesting ones have been picked up and translated. I'm sure there are plenty of cliché and horribly written webcomics. They just haven't been translated.
Why webcomic have been so popular recently?