Requires more battery, clear sky views, etc. The benefit of AirTags is that the sensor network is terrestrial and the energy and comms requirements are offloaded to the sensors.
Try to do it yourself. You would quickly find out what it is not a reliable method.
And AirTag costs $30 or even $25 each in a 4 pack.
With AirTags, I think we have reached that tipping point.