My educated guess is that the Weavers sold a fraction of what the Kingston Trio sold, as the trio were Capitol records second biggest act of all time, the Weavers were of the pre-baby boomer generation and their fans were dwarfed by the trio's fans in sheer numbers. More people heard Dave Guard and learned that Pete Seeger and the Weavers even existed because of those big Kingston Trio days. Just like Martin guitars was carried for years by the Trio, more people got turned on by the banjo and sought out people like Earl Scruggs because of the Kingston Trio, not Pete Seeger.

I am not saying that the Kingston trio were the greatest thing that ever happened and that a) no Weavers, no Kingston Trio, and b) no Pete Seeger, no Dave Guard, but the Kingston Trio touched much more people in sheer numbers alone, hence their more important influence in the popularity of the banjo.