And I either don't have any incentive to follow them, or I already know where they are going before they do.
Most clueless CMDRs select the closest system on the list, or the nearest system with a suitable starport. In these scenarios chances are that I already have a route plotted and will get there before they do (I'm not fumbling with the nav panel, I'm charging my FSD the moment I see their hardpoints retract, and almost no one will load the next system faster than I will). Not that it usually means much as I rarely pack an interdictor (I see it as almost as useless as the wake scanner...submit+high-wake is entirely too easy. I haven't lost a ship in an encounter where an interdictor was involved since 2015, as the very act of interdiction voids any chance of catching someone off-guard), so unless I can hit their destination before they do (rare, but it does happen), they escape.
I reject the apparent implication that KBM provides an overall advantage in combat. Regardless, I'm also not going to need a wake scanner to follow those who are on my friends lists, who aren't going to retreat, or who want to be found.
That's the point...the wake scanner doesn't have any real niche other than harvesting data. NPCs suck and CMDRs either suck or can easily defeat attempts to follow them via wake scanning. The combination of persistence issues (a low wake vanishes if no one is holding the instance it's in) and the small interval between jumps foil almost every scenario where wake scanning would actually be useful.