It's actually hard to know if a different attitude by law enforcement would have turned up a lot more cases before the 1990s. It would depend on the number of homosexual men actually in the priesthood at a given time. Before the aftermath of the Second Vatican Council ("Vatican II," 1961-65), seminaries would simply reject a man if he didn't seem masculine. Like the military.
But that began to change at seminaries after Vatican II, plus the influence of the western "Sexual Revolution." That didn't go well. Nowadays, many seminaries and orders have gone back to the old model, screening out poofters through psych and behavior evaluations. Meanwhile, other seminaries in liberal dioceses are still lax because they are afraid of the highly political "lavender mafia." They will reap the rewards of cowardice.
Not all of it is homosexual.