Besides, it makes financial sense to ransom prisoners rather than killing them. Of course if the main attraction for you is the sort of adventure that you go on a killing spree, then too bad for you. You are the one missing the chance of a hefty amount of booty. The name of the game is adventure. Treasure is the means not the ends.
Characters get their hands on a lot of loot but usually they spend it even faster.
A typical adventurer can spend as much money in a week of carousing than the average labourer earns in a life time. It is not easy to horde vast amounts of money around. There are no banks, certainly no interest, and you can't very well carry around 100 pounds of gold and silver everywhere you go. It is possible for you to bury the treasure but there is always the danger that someone might see you bury it or that the place you buried it is occupied when you get back. All in all, you are better off investing in your own ship, keep , etc. or just spending it.