I don't think that has anything to do with field of view. It's just that higher res = higher cost so they can't afford to have high res global coverage at LEO.
It really does have a lot do do with field of view. High res satellites fundamentally can't image a very large area (that's how a telescope works). They also usually can't image continuously. (High res means you can't image at the rate you're moving without significant SNR drawbacks - you have to stay pointed the target so that you have a long enough exposure time. You can get around this to some degree, but either way, high-res sats are designed for bursts of targeted imaging.)
You need _way_ more high-res sats than are currently in operation to image the entire land surface of the planet even yearly. So, yes, higher cost, but probably beyond what a company like google could pay. (Think trillions, not billions)
To emphasize on this: WorldView 4, which has ~31cm pan imagery came to a cost of about $850M. And is the size of a school bus. Vs the significantly smaller and less expensive stalites Planet uses. And unfortunately that stallite had a failur and only was usable for a bit over 2 years. High res satellites are really hard still.
You need _way_ more high-res sats than are currently in operation to image the entire land surface of the planet even yearly. So, yes, higher cost, but probably beyond what a company like google could pay. (Think trillions, not billions)