The British nobility did not traditionally divide their wealth among their children; they left all of it to their heirs–usually their firstborn son. If they had no son, their entailed estate went to the next closest living heir and that was all pre-determined; there was no choosing an heir. (Certain things could be willed to those who are not the heir but that’s a topic for another time) A younger son may inherit a lump sum when he reached adulthood, or he may receive an annual or month allowance. Sometimes that was enough for him to live off of, thus freeing him to enjoy hedonistic pleasures. However, most younger sons needed an occupation unless they inherited an in-entailed estate or money. They often became officers in the Royal Navy or army because they were educated. This was crucial when needing to read orders and write correspondence. Many became involved in the law as barristers, attorneys, and magistrates. Occasionally I hear of a younger son becoming a physician, but that seems to be rare. But for now, I will focus on those who don’t have to work in an occupation for a living and who have a large estate for which they are responsible.
Wealthy landowners such as Mr. Darcy spent a great deal of time managing their lands. Think of it as being the CEO of a multi-million dollar corporation. Yes, he has upper- and mid-management, in the form of solicitors, land stewards, and workers, but he had the responsibility to care for a huge estate which usually included many different locations, houses, lands, and tenants. Think of it as owning a whole bunch of rental properties with tenants who constantly needed repairs and help with all sorts of things which affected the overall prosperity of the estate. He might also be involved in investing and buying or selling properties which might involve travel. How he managed the family estate would affect generations to come, a heavy responsibility to shoulder with much at stake, so most took this seriously.
In addition to caring for their estate, most landowners were involved in politics. If they were titled, they were expected to serve in the House of Lords. If not, many served in the House of Commons. Parliament met for months at a time, which took them away from their lands in the country. Those who served in the House of Lords could be called into serve as jury if a peer went to trial.
So even though a number of them did enjoy hedonistic pleasures, an honorable landowner’s life was not all fun and games, not even in the summer.