The main differentiation is that the app is multiplatform. That is, it works on the web + mobile apps while the majority of the $5 once apps are only in one platform. The other major point is that most of these apps get abandoned. Developers put it out there to try to fish some cash after the initial versions and never put more work into it afterwards. The idea of the app having a yearly subscription model is to sustain the development and get more features and value with time.

There's a big part of the audience that'll consider saving $6 for a one time payment, but thankfully there's another big part of the audience that understands that projects need to be sustainable in the long term in order to get constant improvements and are willing to pay for a yearly subscription model to make sure the app will still be out there in the mid-long term!

Also, there are many free habit trackers that are way better than those charging $5 imho! So price doesn't really define value :)