alt Hacker NewsThe problem is that those are treated almost like an app, you need a $99/year developer certificate to publish them.
Many third party ticketing solutions venues and events use do support this, but for instance if you want to sell tickets for a party and self-host, you need another external integration, or a developer account. Generating a PDF with a QR code, and publishing an .ics file is essentially free.
My guess is that the are requiring this in order to reduce the amount of fraud there (I am sure there still is some, but...). Apple really does not want to be involved when someone can't get into the Taylor Swift concert that they paid some scammer a lot of money for the Apple Wallet ticket they got.
Having an authenticated developer account at least provides some level of speed bump to scammers, and a better starting point for the police.