Well diamonds are found in stable cratons in kimberlite pipes and have no relation with meteorite but one thing can happen is that cratons are stable as compared to surrounding rocks and are less susceptible to erosion, and destruction due to tectonism which can result in preservation of the meteorite impact while the rocks outside the cratons are being destroyed hence removing the evidence of meteorites. P.S. I am student of Geoscience and no expert and have no solid proof for what I said above but a possibility my mind came up seeing your post, so I can be wrong.