What the end user often forgets is Apple does billions of dollars worth of market research and user statistic collections that influences the design of their machines.

When the hardware engineers were deciding on whether to put in a smaller heat sink or not they likely looked at the usage stats of the M1 Air and discovered that 0.001% of people use it for editing 4K, 10bit video in Final Cut Pro so they could afford to cut those potential customers out of the loop because the vast majority of people would never notice any thermal throttling.