In The Devil's Star, a thriller by Jo Nesbo in the Harry Hole series, a series of four murders were committed, in which 3 victims were young women, 1 was a young man. I searched my heart and, to my chagrin, had to admit that the death of the young man seemed less "thrilling" (or what the Chinese call 惊悚) than the women's. Perhaps because I am a woman, the murder of a woman seems more identifiably terrible to read about. Why do men like to read about murders of women, especially a young, pretty woman of reproductive age? Maybe this is a belief or instinct buried in all humans --- women are a more valuable/precise/scarce resource than men to our species/tribe, thanks to the inefficiency of childbearing. Every woman is needed in the game of reproduction for the tribe. Instinctively, we feel a greater loss in a woman's death. The same reasoning goes for our feelings toward the untimely death of a young person versus an old one.
Also, yes, murders with a sexual motive thrill readers a lot more than murders for money. Financial motives were once common in "cozy" mysteries, in which one has much room to play with the issue of inheritance. Social changes have rendered those stories obsolete, even if homicide for money remains common in the real world. What other motives can mystery writers use but sex and revenge? Political murders and assassinations belong in its own subgenre.
Well, frankly, murders for money or politics are just not as intimate and therefore as thrilling as more emotional and personal motives such as revenge and sex (including jealousy and various perversions). It's human nature. The market is unlikely to get tired of them any time soon.