A lot had to do with King John of England. He was, of course, the King who signed the Magna Carta with his nobles in 1215, a year before his death. This occurred because of King John's misadventures trying to rule both England and part of modern France, and the resulting difficulties he had with his (English) nobles (including clergymen).
The Magna Carta went far beyond e.g. the 14th century Golden Bull of the Holy Roman Empire (which guaranteed noble and church representation in government). The Magna Carta protected nobles personally, not just governmentally, against arbitrary taxation and feudal levies, and illegal imprisonment and sentencing without trial by jury.
On the other hand, the Golden Bull of Hungary in the 13th century perhaps gave too much freedom and power to the nobles. This protected the nobles against the king or queen, but allowed them to oppress the common people. By accident or otherwise, King John, whatever his other faults, managed to strike just the right balance, as discussed in the next paragraph.
Ironically, King John championed the cause of (free) "common" men against the nobles. Some of his policies against the nobles were a milder version of the "Reductions" (of noble land and power) undertaken successfully by Swedish kings in the 17th and 18th centuries. John also made it possible for "freemen" to sue the nobles and win, setting important precedents in "case" law from cases that he personally decided. ("The enemy of my enemy is my friend.") Thus, he offered common people a measure of protection from nobles (unlike the case in e.g. France) even as his signature on the Magna Carta put limits on his own royal power vis-a-vis the nobles.
The Magna Carta was reaffirmed, if modified, during the reign of his infant son Henry III, and it is this "modified" form that has remained in force. King John started his family late in life, which may have offered another important advantage to the nobles.