Sure, but touring is not very cheap either. It seems to be pretty common with bands from either America or Europe that can tour pretty frequently on their own home turf, but when it comes to crossing the sea, it never or rarely happens. It might be hard reaching success on both sides, especially if you are a smaller band. It's interesting to me that some bands who have been putting out quite a few albums by now (TDH, Dredg for example) haven't really toured much (or at all) outside of US. On the other hand you have bands like Periphery who have only made two albums, but already toured all over the world.
So I think with the case of TDH, they are just a bit too unknown, or makes the kind of music that not a lot of people listen to. We love them here on DTF, and a lot of people into either indie or prog might know and love them, but even if they did a small tour by playing the smallest venues, it would still cost a bit.