[ldunn]

Er, again, fine, but this has nothing to do with the question of "how can something so hard to detect be so abundant". The question isn't "should the non-detection of dark matter decrease my credence in it".

It's of course true that the continued non-detection restricts the available parameter space. But there is no physical principle that says that if something is as abundant as dark matter it really ought to have been detected by now - it's not as though if something is as abundant as dark matter, then it really needs to have some minimal coupling to baryonic matter that the existing experiments are now ruling out. Dark matter can just be really very hard to detect, there's no issue of how that "can be". Things that can change the rotation of galaxies are not obliged to be detectable by 2025.

If your weighting of the relative probabilities is such that you feel you should be going to bat for MOND at this point, that's your prerogative. But it's not related to the question that was asked.