It's not like everyone buys it on the same day, and never buys anything else from them. If they don't fix security issues new customers will refuse to buy the product.

Besides in the old days you could still buy a "maintenance" agreement for your product, which entitled you to x months of upgrades. You would still own the licence, though.

I don't need security fixes for Lightroom or Photoshop... Like my camera is not going to start hiding viruses in photos all of a sudden.

It has less to do with your camera injecting viruses. There are other attack surfaces. For instance someone could send you a malicious Jpeg and if your Adobe application has a vulnerability and you decide to open that file, it could be exploited.

Sure, but I don’t use photoshop or Lightroom for images I didn’t create.

As Khaled Mardam-Bey recently discovered.