It is one of the most difficult feats to achieve.RG and W were far more different than now, so it is much easier now to do it than in Borg´s time.Nothing to see at all.
Bjorn explained in his book that some factors helped:
1/ He had an amazing footwork which allowed him to reach amd make great passings even off low and por bouncing balls
2/He got menthally prepared as nobody else.His superb concentration would not allow him to get angry or frustrated over low bouncing or non bouncing balls
3/He was not a natural volleyer.He just " put" the racket but, on that grass, his drop volleys wouldn´t come back.The other way round, at the hard courts of Flushing, those drop volleys would be easy to chase down by a Mc Enroe or a Connors, to name a few.
4/ His fantastic body would not get too tired or spent at all at Roland Garros, so he never reached the Wimbledon courts too tired or burnt out.
5/He had great help from amaya,Edmondosn,Teacher or Amritraj, the guys that almost beat him in the eralier rounds at Wimbledon.By that I mean he just had to concentrate on from the beggining and those guys helepd him peak at the end of the first week.usually, Borg played his best grass court tennis in the third, fourth round and quarterfinals.If you look at his stats, that is a fact.He overwhelmed anybody in round three, fourth and five, while he suffered in round 1 and 2.In the semis and final, of course, he was tunned up but so was his opponent and, depending on style of playing, he could be troubled or not.Mac Enroe,Tanner,Ashe,Gerulaitis, had the kind of game to trouble him and put him to the limit.Nastase,Connors,Vilas and Okker not.