They are not saying the EU is the root cause of the failure, just that they cannot close the hole currently due to the EU.
What they leave out is that they could choose to integrate Defender into the OS for free, thereby removing it as a product to compete against. They could also move Defender to not require kernel hooks either. Neither are options they want to consider currently.
No comment about being able to move Defender to not require kernel hooks (I don't know).
Two reasons:
1 - Few people understand anything about how their computer (/car/stove/phone/medicine/...) works -- they spend their time on other things.
Without any model of how their device works its easy to misassign responsibility (see how many people think that Safari is Google or vice versa). So it's in MS's interest to try to get the message out. Of course people do this when they are at fault as well.
2 - EU is in a wave of beating up* on certain large companies. This can also be an opportunistic way to push back.
* I am not implying whether I think the EU is correct or not.