No reason that general purpose computing platforms should be treated differently. I only bring that up because it's a common response to why Apple should be punished/fined. And general purpose computing platforms isn't even properly defined by a government body.
With a Tesla, I can be doing anything while I supercharge since it is downtime I must endure. I have posted to social media, watched YouTube, play games, read news, done zoom calls literally on the car's touchscreen. So why not open that up too?
No idea why people keep using that as an argument. No one said Apple is being forced to. Apple made this business decision well over a decade ago. There were no laws about "general purpose computing platforms" being forced to be open. Seems very arbitrary that Apple is punished for being successful.
Apple has made a lot of "business decisions" since the iOS App Store opened in 2008. Many of those decisions were harmful to developers and thus customers.
The most damaging decision was forcing developers into the "Family Share" revenue model in 2014, which forced developers to provide up to 5 copies of an App for one purchase price.
When the store opened in 2008 it offered a reasonable business model to develop mobile apps that cost "a few bucks", but that "few bucks" would be multiplied by the number of mobile devices that everyone eventually carried with them. This was not new, and something Microsoft was attempting for years with near zero success because the devices, and Windows Mobile sucked. The iPhone & iOS was much better so it gained traction.
So it was reasonable to develop mobile apps because the development costs were less than the costs of developing more complicated desktop applications. But development costs are never zero so there is a minimum amount of revenue needed for each device install. This was working well for many developers with viable apps up until 2014.
When Family Share came along it was NOT optional. If developers did not accept the new app store agreements they could not renew their developer account so at the end of their annual membership the account would lapse and all their apps would be removed from the store.
The common response to this criticism was no one was forcing developers to publish on Apple's app store, but this neglected to consider the number of apps already in the store that were developed with viable business cases which relied on the "few bucks" per pocket revenue model.
When companies take actions that harm markets, government ends up getting involved. My basic beliefs are this is not initially a good thing because governments are incompetent and just screw things up more. I've also come to accept this ultimately motivates companies to "let go" of their idiotic desire to control everything. The EU has begun to define market concepts such as "Gatekeepers", and regulations to limit their conduct. At some point we may see them define "General purpose computing platform" and regulations for them. This will end up costing everyone, including Apple more and more revenue until Apple realizes the only way to resolve the issue is "let go" and allow iOS apps to be distributed just like Mac Apps.
NO government or court jurisdiction is pursuing Apple for how Mac Apps are sold.
All of this will continue to get worse until someone at Apple realizes this and decides to "make all the BS go away" and just treat all their platforms like the Mac.
But Apple has let their "control freak" personality take over their rational brain, and now all the new EU app store features / agreements / polices are just another crap salad developers will have to sort through - this pushes them towards how Microsoft screwed up the mobile market from their beginning. It will be a long time before Apple remembers they make money selling hardware so that rational brain will be absent for a while.
Edit: imagine being a new mobile developer with a new idea looking at how to monetize your App in the EU. How many will look at all the new regulations and Apple's contorted polices to deal with them and just say screw it?