hard serves because they were easier to judge. The float serve (when done right) were very difficult and back then you had to bump the serve which made it really hard. Also when you go up and try to kill a set you are more prone to a hitting error than just a good solid hit. It doesn't take a whole lot to send the ball down hard. I'm not thrilled by all the service errors but when you are aggressive they happen and you need to serve strong or you will get spiked out of the gym. Unfortunately the float serve is now not as potent as it once was since you can volley it - which I don't understand, it is a carry or double hit every time. There is almost no way to volley a true "float" serve without catching it with one hand first which is technically a double hit. It was obvious when you bumped them. But a lot is different now from when I played.
But it's still not just who can hit the ball the hardest but who can make the most hits count. Last week we beat Hawaii by Langlois hitting the ball to where they weren't not just hitting it hard.

Just an interesting observation, I notice nobody hits lefty and righty. We used to practice switching arms so you could throw the block off. You would see a guy draw one arm back, rotate it around and bring up the other arm and hit the ball. It was not easy but some guys were pretty good at it and so not only did you have to try to read line or angle, you had to try and figure which hand was going to hit it because it was a 6 inch to 2 foot difference and a different angle of the ball so it had a better chance of tooling the block or sneaking through (but not me I was a setter )