The platform must have any of the following to be a DMA gatekeeper:
* Market capitalization of at least €75 billion.
* More than €7.5 billion turnover from EEA residents.
* At least 45 million customers in EEA.
* At least 4.5 million business customers in EEA.
Once any of those criteria are met for 3 years, they qualify as a Gatekeeper. While the gaming market is massive, any individual console platform still sits pretty comfortably below those criteria. You can find the customer number by googling around a bit - Xbox only has around 3 million active customers if I'm not mistaken (counted by Xbox Live accounts that were active in the past year).
A platform truly needs to be collosal to be considered a Gatekeeper. This law is specifically for the large platforms, not small fry.