I bet their telemetry shows that a lot of people grab a quick charge while in the shower or the like, and that 10mins is a good amount of time for that.

Or put another way, past ten mins it’s just as likely the phone will be plugged in for hours or overnight and the charge speed is irrelevant.

Also, it may be to avoid overheating the phone. Otherwise you might expect to see a GAN charger where the body is a heat sink.

That should be on the phone to increase its own resistance and slow down the power intake.