Also, Pete hardly ever played on clay until he turned pro. Nadal, Borg and Federer grew up playing on clay as did many of the European and South American players.
I was far from a Sampras fan, so I don't care about making excuses about his failure to reach a final at RG, but that is a very good point.
The likes of Federer, Becker, Edberg, Stich, Ivanisevic etc. all grew up playing on red clay in Europe, and McEnroe grew up playing mostly on har-tru at Port Washington, and a lot of notable Aussie players grew up playing on tout cas which was a clay-equivalent surface.
Connors grew up playing mainly on fast indoor wood courts before moving to the hard-court dominated SoCal at the age of 16, but he still played a lot on har-tru as a kid and junior player (the US junior scene had a lot of har-tru events back then). Plus while he was an all-courter rather than a strict baseliner, his baseline game was more suited to clay than Sampras.
Sampras however was one of the few high profile attacking players to grow up playing on the hard courts of California, and had significantly less exposure to any type of clay as a kid or junior player. As a result his movement on the surface wasn't particularly strong (especially compared to how well he moved on other surfaces). Plus while he could string out excellent victories on clay, he never had the ability nor stamina to string out a series of them in best of 5 matches on the surface to win the RG title.
Obviously 1996 was his best performance there, reaching the semis before running out of gas and having nothing left for his semi-final against Kafelnikov.
In 1994 he entered RG looking to hold all 4 majors at the same time. He was at the absolute peak of his powers and height of his dominance, and had just won the Rome title under the coaching of Gerulaitis. But even then I felt that Bruguera, Courier and Medvedev (who won the Monte-Carlo and Hamburg titles) were big title favourites ahead of Sampras that year. And Courier stopped him in the quarters before going down to Bruguera in the semis.
. There's no real justification for lack of a French title, but I will say that he was the best player of his generation playing a style that didn't reap any rewards on clay which is a fine trade off. In other words, he has 14 slams which is to be commended, and would very likely have less had he slaved away to try and win on clay or adopted a better style for clay. 
