My guess is the following:
AdNauseam harms Google much more than a „classical“ blocker. The biggest problem I see for Google is that it dilutes / damages Google’s main asset (its database) by clicking on all ads on every page. This is fundamentally different from getting less new data.
The other thing I don’t really know about is whether Google in this case has to pay for the fake clicks (on the blocked ads). If so this would put them in a bad light vis-à-vis the companies that pay for the ads. And it would be worse than registering an ad as blocked and not transferring money at all.
Moreover AdNauseum is a relatively small fish, so nobody outside of certain circles notices or even cares about this decision. The complete opposite is true is for AdBlock & uBlock Origin. These tools are very popular and wide-spread (also in professional circles), not only for blocking ads but also as security measure to avoid malvertising. A ban would create a massive outcry and shit-storm, potentially driving individuals and professionals away from Chrome altogether.
Last but not least: the long-term game is mobile. Risking a shit-storm in order to get some more desktop users to delete their blocker is not worth it when the majority of traffic comes from mobile devices that don’t even allow blockers.