It's poorly worded. There aren't three motors per axle, there are three motors total: one on the front axle and two on the rear axle.

The translation's a little woolly.

For the AMG GT4 there will be 3 motors: two at the rear, and one at the front.

My interpretation (and my German's pretty lousy) is that each motor is combined with a gear system in a single package, and they're calling the overall package (motor plus gears) a High Performance Electric Drive Unit (HP.EDU).

The two rear motors will probably be independent, so no need for a mechanical rear diff (it'll be electronically controlled).

There's no mention of a front diff, so it's unknown whether that's built into the front HP.EDU or is a separate mechanical diff).

To build on what others have said. Multiple motors per axle allow you to get rid of the diff, and you get torque vectoring basically for free.

Then there's braking. More driven wheels means more braking energy that can be recouped via regen. In traditionally rwd cars you lose out here because braking energy tends to be directed forward.

Also there's packaging. One large motor might impinge on the cabin.

Also you get benefits wrt mass production.

A smaller motor is easier to handle. Potentially could avoid the need for high voltage cables. Which eases repair.

I got the impression that there were three motors altogether and they were integrated with the axles.