As a WP dev, as mentioned above, the biggest problem is the promotion and actually making money from the apps.
I have my 2 WP app published, one has 31 downloads after a year, the other one 7 after a month now which gave me a total of $0,005 revenue
But perhaps the problem is with not enough promotion effort from my side, after all for me it's just a hobby, not a full-time job. Who knows...
But what was the most annoying for me is the publish process. For some reason, you can make the app work perfectly in your debug environment, but then when it comes to the certification process, suddenly a fully working debug app behaves completely different in the release mode. After 2 publishes I know how to handle it now, but for the first time it was a major pain in the backside and it took me like 2 weeks to get it solved.
Best regards,
Keran