Players aren't going to spam probes. Because it takes a while for a batch to reach the planet. Players are motivated not to have to wait for the next batch to become available. Their pay off is time.
From the live stream it looked like you could only send out a batch of 3 t any time and let's say they take 30 seconds to do their thing*. For a par 5 planet that means you can scan it all in about a minute if you are good. if you have to carpet bomb it with 30 probes then it takes at least 5 minutes. That time soon adds up, especially in the larger systems.
*these figures are guesstimates based on what was shown and are for illustrative purposes only.