The difference is you cited software projects, not hosted infrastructure. A person can contribute to a FOSS dev project and not incur expenses dependent on end-users activity. Hosting a fediverse application isn’t like that, somebody has to pay for the hosting and the hosting expenses will scale with user activity.
And what is it with the narrow aspects? I totally get the need for mobile support, but the default desktop view looks like it’s trying to play nice with old 4:3 aspects. If that’s the root design goal, I sure hope we can let that design goal die. In a 16:9 maximized window there is so much wasted real estate it pains me.