Yehuda Tzvi – I’ve also wondered why the ratio of Cohanim to Leviim is so high. I believe there could be two answers:
1) This won’t go down well but a lot of Cohanim nowadays are probably not bona fide Cohanim. There is a story brought down about one of the Gaonim (I think Rav Saadyah Gaon) who gathered hundreds of Cohanim to circle Yerushalayim as a way of hastening the Geulah and he saw a vision of Eliyahu Hanavi who told him that only one (incidentally lame) Cohen there was a real Cohen. It is also brought down that the Vilna Gaon would repeat Pidyon Haben on himself every time he met a new Cohen – until he met a Rappaport Cohen.
2) It could be there are many more Leviim around not realising it but their status as Leviim was forgotten. In contrast, Cohanim have had a unique way of preserving their identity through the generations with Birchas Cohanim.