They'll come here when they get offers from clubs that make it worthwhile to do the tour. That hasn't been the case for a while. They could set up a Kickstarter/GoFundMe account that would help cover the risk of the tour the way that Ne Obliviscaris has, but really it's a matter of opportunity costs as much as expense. The European market is better to the band and likely will always be so. That said, you know that if Amo does tour the US again I'm in for tickets and merch no matter what.