Selling 10k more or not is a difference.
That's also something I don't understand, why did they stop releasing DVDs. I'd understand CDLs, but tours?
Selling 10k is still a significant amount and generating a good income. DVDs are expensive in Japan after all.
And there are a lot of artists still releasing live DVDs selling the same or less than Ayu and still doing it regularly. So not being worth it can't be a reason.