In this context, it's something that requires a lot of work for little reward. I think it's similar to "dogging" something.

It actually has a context in marketing for products where you will have a small stake in a shrinking market:

https://www.marketingstudyguide.com/wp-content/uploads/2015/...

In UK/Commonwealth parlance, "Dog" means terrible or slow. "Dogging" is, erm, something very very different and NSFW.

In British English "an absolute dog" can be slang meaning "extremely slow", e.g. "this 386 runs like an absolute dog, compared to my Thread Ripper".

My best guess is that's how GP was using it.

I assume as in "gone to the dogs" - meaning gone bad, got awful, isn't good anymore. Old expression, came from (IIRC) when human food went bad and was only fit to give to the dogs.