That is true. Thinking about a way to get an idea of the size of the problem I tried to find maps showing lightning activity, even if the lightning that could be seen from space would not be ground strikes, but cloud to cloud, or better cloud to air or even space, like sprites:
The NASA information page on SEVERE WEATHER 101 > Lightning Types has this:
It seems to be easier to encounter maps of the ground strikes. Here is one from an article in IEEE Spectrum
And a Russian map that did not explain what type they counted.
On both of the two previous maps, the landmasses and nearby areas stand out, but I wouldn't say that is very clear at all when one takes a second look at the map with the satellite observations. If the cloud to cloud and cloud to space follow the patters of activity over land, as one might expect, then the map most be showing something.
Next, one could try to calculate the area covered by the satellites. Here is one map with a semblance of coordinates.
Comparing the two previous maps, one has an idea that most of the measurements appear to be within 180 West to 15 West longitude and then from 50 South to 50 North latitude. Next, one could ask how much of an area that would be compared to the whole Earth and also if the satellites can register the flashes in daytime or how strong they would have to be to make that possible?