The first thing that comes to my mind is why would a
company not want to get some free advertisement? Basically, they get free advertisement whenever the user posts in a non-paying board. Why would they want to give it up?
Economically doesn't make any sense. As for
local language specific signatures that makes a lot more sense... E.g in the case of chipmixer they can have as many translated versions of their signatures as they like... In the recent
hiring they wanted German posters, So a german specific signature would have suited them in
theory but if you look at surveys,
they suggest 56% of germans [1] can understand English. So is it worth paying for the translated version of their sigs is their marketing decision as you said... But this could work in other local boards where the native speakers hardly understand any English. I don't see why something like this shouldn't be developed. It will open up all sorts of advertisement opportunities... This could be further developed for forum Banner ads e.g Each local board could have their own specific banner ad. Opening up more spots for advertisers basically... It's a plus one from me...
Source:
[1]
https://en.wikipedia.org/wiki/List_of_countries_by_English-speaking_population