There’s a difference between boycotting and choosing not to advertise with certain people. I worked in marketing for a while and we would often get reports that our ads were seen in places we didn’t want them to be and that were supposed to be on our “blacklist”. That wasn’t a case of us boycotting, it was a case of us not wanting our ads in certain places. We would contact the people responsible and it would be sorted quickly. So I can fully believe that these companies didn’t actually intend to have their ads shown on GB News.
I did once try and push through a boycott of The S*n when the phone hacking scandal was happening. Felt especially pertinent as I was working for a phone company so hoped they might pay attention. But our agency had a deal with The S*n and so we couldn’t back out as it would have caused issues for the entire company. So it never went to the client as far as I know.
Anyway, my point is, these companies are quite possibly not boycotting, they just didn’t want to be there in the first place. And there is a difference.