Cloudflare has been controversial for dragging their feet when it was time to stop providing protection to nazi websites like The Daily Stormer, 8chan and Kiwi Farms. Also the Taliban, ISIS and so on More about this.
For this reason, a lot of fediverse servers do not use CloudFlare.
Yes, I have built it as a website app also and that is the primary UI. The mobile app is just a read-only viewer for quick access to the information people need on the go. It's not entirely pointless.
A lot of people don't know how to install a PWA (which I also provide, if they want it) and have never done so. They also just expect there to be an app in the app store and when they hear about a tool someone else is using that's their first port of call.
I built an app like that. It uses a WebView, although all the HTML is self-contained and it only accesses the internet to make API calls.
Mobile app development really sucks, as a developer. The frameworks, the build tools, the specialised languages that can't be used anywhere else - it's a hot mess. Making an 'app' using that method is much quicker and easier for me because I get to use HTML, CSS and JavaScript, which I already know and have the tools for.