Why the import/export system?

[Cwpute]

I've been using this app for quite some time and wanted to automatically back-up my notes using DavX and a Nextcloud server.
Unfortunately i discoverd the notes were not saved as plain files, but had to be manually exported before being tampered with by other apps.

A simple question: why?
What makes keeping these files inside the app better than saving them as plain files to begin with ?

I'd hate to see my notes being lost because i didn't back them up manually for a week, while the rest of my contacts, mails, photos etc… are automatically handled by my backup setup. Keeping the notes locked into the app behind an import/export system seems strange and counter-intuitive to me.