With no 3-point line, there was no incentive to shoot the ball from that distance. Without looking up historical stats (looking to you, Indy), I would venture to say less shots were taken from that range before. That means more shots inside the 3 point line. Shooting percentages are higher for such shots, potentially offsetting the the additional point from the 3 point line that is made at a lower percentage.

And this obviously says nothing about the brand of basketball played in each era. Officiating has tended to move towards favoring the offensive player. Offenses (especially BYUs) seem to be a bit faster paced leading to a higher volume of shots.

Comparing players decades apart, especially when it comes to pure point production, isn't an exact science.