Because the thermal throttling is a non issue. Go look at comparisons of last years M1 models. The battery life difference is only 2 hours. The Air, however has fast charging which allows a 50% charge in 30 minutes. That’s 9 hours of battery life in 30 minutes.
The M1 MacBook Air thermal throttles after 10 minutes of sustained load with a performance loss of 15%. So basically you are paying for a M1 chip which you cannot even fully utilize if you are actually using the full capabilities of this thing.
That is not a non issue and a big advantage that the 13” MacBook Pro has.