Oh, this thread is the one that
@Mem was talking about.
You've opened this thread since last year
@GaryA ? Wow, i'm way behind here.
Okay, so this is the topic of hotlinking which has existed since the early days of the internet. But back then it was more about bandwidth issues since the internet pipeline was small. Websites did not want you to link their images stored on their server, unless you visit their site. The classic example of this was Adobe, since Adobe back in the day was the premier tool to build sites and they also had their crown jewel: Adobe Flash.
With the invention of HTML5, Adobe Flash is now in the dustbin of history and more importantly the internet pipeline has increased since we're all on high speed internet.
So, nowadays it's not about bandwidth but more about control and trying to force-direct users to visit the site where the images are stored.
Facebook is a great example since they want complete control of their site experience and they don't like to allow hotlinking of images.
TLDR: Hotlinking has been a thing since the early days of the internet and it will probably continue because web owners want control.