Revisit is getting better and satellites have an edge when it comes to total coverage of the earth, but the 120,000 flights around the world each day typically fly predictable routes at low altitudes near urban centers (takeoff and landing). This presents a massive opportunity to leverage all of that "free energy" and use aircraft for earth observation. Coverage can be supplemented with satellites, but revisit of aircraft is far greater for many terrestrial locations.
2x/day revisit for most of the world is probably sufficient for the majority of use cases, but that assumes good weather (for images). On the other hand, LAX for example sees hundreds of takeoffs and landings each day, so if you were interested in modeling retail foot traffic by parking lot volume, pace of urban development, rate of containers moving in and out of port, etc. you could get a massive boost in temporal resolution using aircraft and far cheaper than launching + maintaining a satellite constellation.
Maybe, but aircraft tend to follow much stricter paths than one would normally believe. Particularly around urban centers (airports) they queue up and only really fly a few routes through the area. On clear nights you can often see the lines of nav and landing lights forming as aircraft approach the city.
2x/day revisit for most of the world is probably sufficient for the majority of use cases, but that assumes good weather (for images). On the other hand, LAX for example sees hundreds of takeoffs and landings each day, so if you were interested in modeling retail foot traffic by parking lot volume, pace of urban development, rate of containers moving in and out of port, etc. you could get a massive boost in temporal resolution using aircraft and far cheaper than launching + maintaining a satellite constellation.