Socially, France was in the process of being transformed from an Honor-based culture to one based upon Rules. This was very much played out in the clash between what nobility can get away with vs. what the rules declare.
Richelieu was very much the point man on the centralization of government and the creation of the modern nation-state. This would play out in full under Louis XIV, but the process of destroying the economic and military power of the nobility in France began under his father (or more accurately under his red right hand, Richelieu). A big part of this was bringing the nobility to heel under the Rule of Law rather than their traditional privileges. Another, unspoken policy was to impoverish the nobility and financially tie them to the Throne by making them spend lots of money and become dependent upon lucrative work either in government or the royal court.
The King’s Musketeers was composed mostly of “gentlemen,” but by and large, they were either “spare” sons, or from the less financially wealthy families and those from the provinces. Along with providing these young men a chance to sow their wild oats, it was also supposed to be an opportunity for them to show their worth and gain a chance at better and more lucrative government and court postings…and politically indoctrinate them into loyalty to the Crown.
Some other pieces of context: