Why do most websites want you to click "next" twenty times just to get to the next screen?

So they can load all the ad crap they want you to see before they show you what you might want to see. These days, I pretty much give up and bail out of these lists because they are so annoying.

I’ve just come from a site where I wanted to see some pics but they insisted on putting them out one by one. So tedious. I gave up around pic five.

I’ve noticed this more and more.
It was annoying but semi-understandable when it was only pictures they were feeding one at a time, but lately I’ve opened some things that were supposed to be lists and turned out to be single page items with totally unnecessary pictures.

I can only guess that the ads change with every picture. Like @janbb I’m ptreey much giving up on them.

Because it takes you a lot more time to get to the content you are seeking and time duration spent on a website is critical for selling ads. If a site can prove they have visitors spending more time perusing their content the more they can earn in ad revenue.

Two reasons:
1) as @janbb said, it’s 20 opportunities to advertise – they can sell 20 times as many ads.

2) network load. if they shoot 20 pictures down to your PC at once, that’s a lot of data flowing, and it may take several seconds to get there, depending on your connection. You might get impatient and move someplace else because it is taking so long.

By doing one picture at a time, you don’t notice the download time as much,

Because you fell for clickbait

People who put advertisements on their page get paid every time the advertisement loads. Every time you click, you load a new page—which means you load a new advertisement. Even if it’s the same advertisement, it counts as being loaded again. So in short, it’s all about the money.