It's a matter of interpretation. From the DMA's perspective, the iPhone is a market and thus Apple has a monopoly on that market. Likewise they consider MS to have monopoly control of the Windows market.
That reinterpretation would have make Apple a monopoly and thus other anti-trust laws would apply, which did not happen. As I said: they are introducing new category, the gatekeepers, for the sole purpose of making the law applicable.
