Social apps like Facebook, Twitter, Tumblr, Skype, whatsapp, linkedin, instagram and so on, depends on people choice.
Other more useful services like local bus schedule, bank app, phone company app, bitcoin wallets, eBay, paypal and so on (some of them may have limited api and apps developed by 3rd party you'll never know if they steal your data)
Music services, meetup app, voip clients, proper tor apps with ui in few clicks, private browsing, smart home applications.
Games, yeah sometimes people play games

And ffs do not tell me YOU don't use any of this, as no one cares about you, phone is made for masses and not dozen who cares about compiling on phone only. As much as I don't like java or android, you can say it "android did it already" almost about any apps, services(like Simpsons and TV shows

And last thing, I'll remind you that official Qt app for conference last year(or was it already this one) was written in Qt for android and that's the version you ended up getting in jolla store. Android version of Qt app on phone officially using Qt as main framework. What else can prove that there are almost no devs, apps and even interest in jolla