Coinomi was open source years ago and we had to make the tough decision of closing it. The developers still contribute to several open source projects. Reopening the source is not completely out of the question, but it's not a simple decision to make either.
That doesn't answer the question of
why it isn't open source? Why, if it was open source, did you decide to close it? You say it was a tough decision, so there must of been lots of factors you considered. What were they?
I'm sure you will always have lots of users, but serious users on this forum are never going to use and never going to recommend closed source software.