My apps generally have been created to solve my own needs and are then provided free for anyone to use. In many cases I see no real need to update them and I suspect even converting them to build in the modern Android Studio would take more effort than I'd care to put into them.
Due to their age, some of them require permissions that were needed at that time in order to perform the tasks required, these days that could be made optional but on the other hand a modern phone could also revoke these permissions.
Specifically for Zap's Abc, the purpose of the app is the convert abc code into midi and/or PDF on my server: hence the abc code is sent over along with a unique id (to avoid clashing) and then the result is returned. As this service was created long before the Let's Encrypt initiative this is all in clear text. At some stage I will consuder upgrading the app, but it has not been a priority.
And now, please read My Privacy Policy in full.