Good question.
Firstly, historically speaking, the nobility have tended to be very conservative in the sense of wanting to hang on to their traditional rights and privileges in the face of modernizing innovations from the central government.
Secondly, and going along with that, the nobility tend to be localists as opposed to nationalists, b/c regionalism also means a free hand for themselves. Hence Northumberland “knew no prince but a Percy” or “Je Suis Le Sire de Coucy.”
The right of pit and gallows gives the lord an enormous amount of social, economic, political,etc. control over their own fiefdom as the source of law. Cross the lord in anything, and he can throw you in his dungeon or hang you. If the lord does anything to you that you don’t like, you can’t take him to court because he is the court.
This is one of the main reasons why kings historically sought to bolster their authority and power through the extension of royal justice. It creates a direct connection between the sovereign and the individual subject that diminishes the exclusivity of control by the local lord, it allows the subject to appeal to the king against the lord and thus allow the king to use the mechanism of the law to punish “over-mighty vassals,” and it creates a popular constituency behind the king that can be very handy when it comes to raising taxes and armies.