Honestly, with the overseas TeamAyu and mu-mo shops available cuz of Tenso, they're probably looking at the metrics of that, and it's clear that a tour outside Japan would simply not be profitable.
It upsets me cuz as a TA member I don't feel I'm getting my money's worth without her having concerts around here. Too many benefits like "at-the-concert-venue-only" lotteries & giveaways, and early ticket sales for TA members, that we in the USA don't get to take advantage of.
Until avex is convinced an ayu concert here would be profitable, they won't do it. And it would NOT be profitable. Ayu's just not relevant enough. Not enough fans have proven they'd spend the money.