Could be, but when the new OS updates every 12 months they can either dedicate a whole chunk of their time updating to the new version, or make it work good on a version that's still going to be supported for 3 or 4 years so they can focus on bug fixes and updates.

Just because Apple can bump out a new OS version once a year doesn't mind these app developers have the same bandwidth to keep up the chase. They have plenty of other priorities.