Why do iPads require a third-party font manager App to install fonts? [closed]

Solution 1:

You are comparing 'desktop' operating systems to mobile, which is not a straight comparison. macOS also allows simple double-click to install a font.

The root cause appears to be that on iOS/iPadOS fonts must be installed using a configuration profile. Fonts from the App Store appear to be already designed this way.
Installing your own fonts does not.

You can make config files for free on a Mac using Configurator 2, but there's no equivalent Windows app, so you'll need to use a 3rd party iOS/iPadOS config generator.

I imagine this is to make removal as simple as addition.

See
Apple KB - Install and manage fonts on iPad
HowToGeek - How to Install Fonts on an iPad or iPhone
HowToGeek - How to Create an iOS Configuration Profile and Alter Hidden Settings