It wasn't.
Most top-10 (and top-20) players were NOT serve-n-volley players (not ace-machines either). The majority were great baseliners, and many of them could actually volley and finish points at the net consistently.
Another myth is that there were only fast hard courts. Wrong. There was a huge variation in speed of hard courts, back then.
Miami for example was always very slow.
Of course there were still SOME great serve-and-volley players too, but not many.
Most top-10 (and top-20) players were NOT serve-n-volley players (not ace-machines either). The majority were great baseliners, and many of them could actually volley and finish points at the net consistently.
Another myth is that there were only fast hard courts. Wrong. There was a huge variation in speed of hard courts, back then.
Miami for example was always very slow.
Of course there were still SOME great serve-and-volley players too, but not many.