it's not about users though. it's about the business relationship between gatekeeper and third parties who want access to the software and APIs and platforms.
if you sideload an app you are still taking advantage of apple's UI, user base, API SDKs, etc. and apple did enter into a relationship with its users which it wants to protect, in terms of security, privacy, and functionality of the device.
if apple wants to protect the enclave, for example, by ensuring alternate store apps use its APIs, that makes sense. this was never about running arbitrary code on iPhone; that's not what gatekeeper status or the DMA was meant to provide.
apple is like 22% of the market in europe. where's all the furor about every other business? the 78% owner also has a lot of issues, but i understand that apple is just so hated for being a company whose products people enjoy that don't get canceled after one year of operation.
also, the DMA doesn't say that apple can't make profit. the EU is still a capitalist society, and until there is a regulation that says what companies can and can't charge for phones, developer entitlements, services, then... there's not much to be done.
lastly, if there were no fees or hurdles or restrictions for alternate app stores then every single large company (not just gatekeepers) would open one so they could plaster their ads, make their own profit, drive users to their own stuff, and basically capture them in their fiefdom. and the DMA makes no provision as to how alternate markets need to behave. i and probably many many others do not want meta or msft or tencent or whomever to steal data, use underhanded business practices, ship shitty code, and do basically anything they want (that apple nor its users could control or do anything about) and that's just wrong.
openness is good, but if the cost is that chrome takes over the world like IE again and that meta can spy on iOS users and drain their batteries like no tomorrow, and force users to use their NFC payment system and secrets manager and whatever other ridiculous crap in order to use their social network, please stop. the DMA has failed if that is the case. we'll head back to the 90s and dumbphone era when you were trapped to use, see, or suffer from terrible and insecure 3rd party applications.
the one thing that cannot be argued is how good apple is at data protection and user privacy. please don't ruin that for millions because spotify wants to earn more money.