There is an assumption here that top grade imaging satellites were used. The images from the Chinese satellites were captured about 24hrs after the planes last contact. This was before the big search began. It is more likely that these were regular geographic information satellites, used for climate and agricultural data collection. This is speculation on my part, but no less relevant than some of the other speculation on here.
If they were SPOT satellites, that are usually used for regular imaging, they work on 2.5m - 20m resolution. Lower resolution uses much less memory and the images can be analysed much more rapidly, electronically. Using satellite imagery does not give instant analysis, sadly, there is a lot of computer data manipulation to make sense of the images (which are to all intents and purposes a data stream).
Modern military satellites can get great images, as they are often put into position to capture a specific image. They are not doing a gradual sweep of vast areas.