Why are third party apps entirely excluded from USB OTG since Android 7? Android KitKat rendered SD cards next to useless for writing, but did not affect USB-OTG at all.

Android 6.0 put USB OTG into read-only, which can be a good thing, but sometimes, I want to write to OTG.

Android 7.0 entirely hides OTG from anything else than Google built-in Stock File Manager,  which is not even nearly as good and functional as ES File Explorer from 2012. (yes, 2012. No typo here.)

Is that for security reasons?  But what if I actually want read/write OTG access?

What's next? Removing Internet access for security reasons?
Though my phone could have Android 7, I've stuck with 6 because of compatibility with a few Xposed modules so I don't know if this helps you, but a file manager named MiXplorer has it's own OTG driver, so maybe it could r/w your OTG device. By default this is disabled, you need to turn it on in the settings.

Please let me know if it did work for you