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That’s probably a majority of the point. Falsely report that some interesting ports are open and he’ll spend time on them and potentially trigger alerts or blocks.
Fake open ports aren’t something a normal user would bother with or understand, but with all the tools available in the nefarious side, it makes sense to have options that make their job harder if you’re willing to use them.
A benign scan could just be looking for an ftp server to connect to or a repeater or relay server of some sort. There are plenty of open services people make available for free and the fact that you would consider it an attack it doesn’t make it one.
At minimum you could be alerted to look for someone attempting to connect to your ftp server with a single basic anonymous authentication vs someone flooding that port with known malicious software attacks, and block the latter across your entire network and effectively ignore the former. Really it seems like you’re advertising your lack of imagination in this context than a legitimate lack of possible uses for spoofing open ports.