I think most of these shows are sold out or close to it though. I think they are just attempting to get back to their roots and regain some of the fans they may have lost over the years. I'm sure they could have played the larger venues if they wanted to. Paramore, when they released brand new eyes, had already been playing bigger venues (like All Time Low) and went back to HOB for one tour just because they felt like playing slightly more intimate shows.
I'm betting the next headliner they play in the U.S. will back in some of the bigger venues, also i bet this album will make them grow even more, even past the pre dirty work high. (that is assuming they lost a little steam after that record, i personally liked the record for the most part, but there were many who didn't)