Obviously there were some people with good style in the 90's, but there was plenty of bad, too. I personally blame:
1. The clothes. trying to skate in size 50 waist, heavy ass denim jorts, bed sheet sized shirts and thick heavy ass shoes isn't conducive to good skateboarding, especially when it's hot out. Throw in a long chain wallet and prepare to eat shit.
2. The boards. Quality control was all over the place, you'd have boards delaminating quickly, shapes were still being experimented with so you'd wind up with something with not enough nose, way too big of a nose, or any number of things that made doing street tricks harder. Wheels smaller than 50mm? GET THE FUCK OUT OF HERE. A lot of times style comes from speed, and you're not going anywhere fast on those bearing covers. Half the time you'd land a trick and just stop rolling cause you ran out of speed or hit a pebble. You also couldn't pop very high, nor could you get enough speed to get you over any distance. Indys were heavier than they are now and the fucking axle would slip the moment you landed primo, and Venture made "ultralights" that even my skinny ass would snap.
3. Progression. I'd argue that skateboarding changed the most in its history between about 1989 and 1995. In that 6 year period we saw vert die and street take over. The industry died and an entire vocabulary of tricks was invented. Things moved so quickly that even the pros of the time couldn't keep up. Often times a video part would be outdated in a year. It was hard to have decent style when you were trying so hard to learn the newest tricks.
4. Media. I can remember not understanding how to do a kick flip because nobody I knew had videos and I couldn't figure it out from the sequences in magazines. I legit thought you did it with your back foot. Most of us were just happy to be landing on the board, we didn't really know what good style even looked like. It was really hard to see skateboarding back then unless you were blessed to see lots of videos or lived somewhere (California) where you could actually see good skateboarding live.