* App approval is a lower bar to pass than App Store approval.

* Alternative stores can have different policies for which types of content are prohibited or for how monetization works. For example, they could allow R18 media, or accept payment via additional payment methods.

* Alternative stores can be cheaper.

* Alternative stores could also enforce their own rules that are superior to Apple's - for example you could have a store that guarantees everything on it is open-source and has been fuzzed, and they could promote that on some sort of a security basis.

But yes in practice "Apple still gets to decide whether you can put apps on iDevices, and you have to pay them for that" does defeat a lot of the purpose of the DMA.