I gave up and quit.
For a few reasons:
First, I got a bit bored. I was tired of writing the same game for the 3rd time. Most of the interesting parts ported over pretty quickly and easily. The parts that were left were mainly fiddling with asset (graphics and sound) formats. And that was no fun at all. (If I was smarter, I might have figured out a way to automate some of the conversions, but they tended to be really fiddly based on how I handled them on the GBA/DS side).
Second, I got frustrated at Apple. I paid them my $100 for a dev license. And then part way through development, they changed their developers terms with a clause that strongly sounded as if they wouldn't approve any apps that were using the 3rd party toolkit I was using. Their wording was just vague enough that it was hard to be sure. Talk about discouraging. I paid my money, was half-finished developing my game, and suddenly they decided that my game might not pass their terms. A few months later, they changed it again, and this time the game would have been fine. But at that point, I was done with it -- I have no interest in trying to hit a randomly moving target of what's allowed to be published.
Third, which was really a result of the first two reasons: my annual developer license expired. I didn't finish the game in the first year, and had to decide if I wanted to fork over another $100 to try again. I enjoy doing hobby development, but I don't enjoy having to pay a subscription to do so. So that was the end of that.
So there you have it.