There are some apps that are designed to do one thing and one thing only, and it might be simple enough where the developer can get away with not updating it for months or even years. For example a note-taking app or an app that curates wallpapers don’t exactly need to be updated every other month, right?
That being said, this could also be why there are still tons of 32-bit apps on the iTunes App Store, but it looks like they could soon be going the way of the dinosaur. In a report from Sensor Tower (via Cult of Mac), it seems that come iOS 11 which should be announced at WWDC 2017, they have estimated that this could end up obsoleting about 200,000 or so apps.
This is because Sensor Tower estimates that at the moment based on their numbers, about 8% of all apps on the App Store are still of the 32-bit variety. While Apple has yet to confirm whether or not they will be dropping support for 32-bit apps entirely, this is what Sensor Tower believes will happen as it will help to streamline their software.
At the moment what Apple requires is that developers who submit apps to the App Store must make them 64-bit compatible, which means that apps that have already existed prior to this ruling are still allowed to exist (assuming there are no updates).