That is because the "after" pictures in the article were taken immediately after all the billboards were removed. They will be (and mostly are already) replaced with paintings, murals etc., better ads, or just better use of the space in general. The options aren't just ads or a bland city.

That's a lot of area to cover with art and it's unlikely it would really fill up most of the space. Also art itself is subjective and people aren't going to like graffiti everywhere either. Things will look more plain, that's just how it is.

Then that is beautiful. I'd like to see those pictures, and the article should be updated to reflect that.

Those pictures don't exist since that didn't happen

I think the "after" images look much better, with the exception of those empty sign frames.