It wasn't uncommon, most websites made by these popular GUI tools retrained these banners,
You're using some narrow definition of "advertising" that doesn't match common use. You don't need to be paid to be a walking billboard.
When the program you were using inserted these it was analogous to license plate frame advertising today[1]. Consumers don't get paid for those either, but it's advertising for car dealerships.
There was also a culture of voluntarily inserting these, but that doesn't mean some of them weren't product placement or advertising.
You're using some narrow definition of "advertising" that doesn't match common use. You don't need to be paid to be a walking billboard.
When the program you were using inserted these it was analogous to license plate frame advertising today[1]. Consumers don't get paid for those either, but it's advertising for car dealerships.
There was also a culture of voluntarily inserting these, but that doesn't mean some of them weren't product placement or advertising.
1. https://www.zazzle.com/car+advertisement+license+plate+frame...