I've never used it, can you explain why you don't like them?

It's basically a spam blog that hijacks inbound referrers from search engines to throw up full page sign in screens and nothing else.

The vast majority of it is effectively stolen and rehosted content.

Everyone else’s complaints are valid (forced signin, stolen content) but my main issue is it’s just completely useless.

For example, I have a project or product in mind and search for something like “pink string lights”. The top three results will be pictures of EXACTLY WHAT I WANT on Pinterest. I follow the link and the URL is just...a picture. No link to a store where I can buy them. No link to a blog talking about building them. No discussion. No question. It’s just a picture somebody saw somewhere and posted to Pinterest (I still don’t understand why anyone does this as there seems to be no community).

I’ve never had Pinterest lead me anywhere interesting or help me in any way. It is the black hole, Debbie Downer, dead end of the Internet.

Is it that much different than Redditors rehosting images on Reddit/Imgur? I find the functional design of the site terrible but there's tons of popular sites that are based on hijacked content.

Imgur is (IMO) turning into the same thing. Banning direct links, forcefully redirecting direct linked images to their ad packed pages of mostly stolen content.

Being so popular and serving images directly seems like a path to losing money

At least in the case of Reddit it's quite different.

The primary value by a huge margin on Reddit is the text content, the comment / discussion section in each thread.

Pinterest is basically entirely built around the rehosted images they pull in. It's by far and away the primary value on the platform. A distant second is the typically small amount of associated text with a given post.

Not really much different, but Imgur doesn't dominate Google Image results. Why does Google make the exception for Pinterest?

they hijack other people's images and when you click you are taken to a pinterest page which is obviously fake (not curated by a human). If that isn't spam , what is, really?

Pinterest always wants me to sign in before allowing me to see anything at all. To me, that should be enough to certainly never show them on the first few pages.