You cannot keep a stationary drone in the sky for long stretches of time. Their field of view is also going to be massively smaller than a satellite. You would need a lot of them just to keep the same amount of coverage.
How do you know nobody is interested in the 'ocean and empty stretches of land'? It could provide a lot of meteorological and geological data for scientists for example.
Funny you should mention meteorological use cases. At a previous startup, we built global historical weather data sets (at 5km resolution, 30+ year hourly time series), accessible via a metered API. This took HPC, storage, and engineering investment about an order of magnitude less than Planet. We also had a whole room of tapes filled with satellite imagery from the world's governmental Met offices...
Our main use case was for wind and solar renewable energy, but we also entertained other uses, like architecture and agriculture. These data sets turned out to be difficult to monetize; while the continental US data set may have broken even, the rest of the globe never recouped the cost of storage, let alone the supercomputer time. It's not that people around the world weren't interested in the data, they just couldn't justify paying for it.
How do you know nobody is interested in the 'ocean and empty stretches of land'? It could provide a lot of meteorological and geological data for scientists for example.