Why do most websites favor "one page" over "multiple page" loading formats?

[Calvin]

Because it's perceived that users (especially those with tablets) would rather scroll through page(s) than click to move to the next static page.

It's something of a 180 from early web design days when 'scrolling is bad' was the consensus design view. The fact that online access speeds are 10 times what they were a few years ago helps in that regard. New techniques, more RAM and new browser display engines also make it possible to have "endless" scrolling that is really just a form of a "windowed view" where what is displayed is held in memory.

Fault the programmer if you have to 'start from the top' when moving forward/back on a site.There are straightforward ways of remembering where users are when they click away and come back to an 'endless scroll' page.