Why don’t mobile web developers have everything on one page

I started to learn web development in art school, but switched to app development instead for various reasons.

I've noticed more and more lately websites on my phone will split up an article into several pages and put like 3 sentences per page. It's very frustrating and at least for me I just find another site even if that other site is less known.

Another thing I've seen more of is putting 1/2 a paragraph of the article and the rest is below the fold under a "tap to continue " button.

I was taught to never deny access to the user, and to me both those things are just that.

So my question I guess is...are the reasons for these 2 annoyances a technical thing (it's easier to load smaller amount of data etc) or is it a design thing?