Space fan here, and I think you are underestimating the size of the task.
Earth has a surface area of 510 million km2.
A plane travelling at 500km/h with a 10km observation track can cover 5000km2/h, or 50000km2 per 10 hour operational day, ignoring transit to/from nearest available airport. It would need approximately 10000 days (28 plane-years) to cover the surface of the earth. I'm not sure what the cost of operating say 7 crewed planes throughout daylight hours for 4 years is, but I'm sure it adds up, even for a small plane. With a crew of 2, we're looking at 56 pilot-years of salaries (assuming they work 10 a day hours 7 days a week and never have time off!) which is running into the millions already, before you even consider fuel or maintenance.
In contrast, SpaceX publish their prices and you can charter a Falcon 9 for $62 million to put 22800kg into low earth orbit. Your satellite only weighs 2280kg? No problem, rideshare deals are available, so your budget would be around 6.2 million plus a markup. Just wait for a near polar rideshare (such as the SSO2 mission scheduled to launch on 2 december 2018) and once in orbit your satellite will travel at around 30000km/h, completing 3 laps of the earth every 4 hours. The earth's circumference is 40000km, so with a 10km track you should be able to cover the whole equator in 4000 laps.
As discussed in other answers, planes are an option for small areas of particular interest, but just as satellites suffer from cloud obscuration, so can planes be affected by the weather, either by obscuration or by being grounded due to unsafe conditions.