>>105372991He did kidnap his wife and hold her against her will in the underworld.
Also, it's because most cultures see death as something not entirely clean or good. Eastern cultures often make people who handle their dead (grave diggers, butchers, etc) into monsters. And the west associates the underworld with Hell, so the association is obvious.
In Greek myth though, Hades was meant more as a sympathetic characters, you're right. Except for that whole "kidnap and marriage" thing. This has something to do more with Hellenistic Greek myth being predated by older forms of Greek worship that we know very little about. Older Greek myth (or Ancient-Ancient Greek myth) had a similar but different group of gods and a heavy focus on worshiping death and the ocean. That's why Poseidon used to be the god above gods because he represented the Ocean, Earthquakes, and the Underworld. And (in a weird twist) Dionysus was at one point considered a near equal with him, because he represented actual death, madness, and some other less agreeable things. Dionysus's reroll into Hellenistic Greek myth was really rocky and took longer than all the other gods, because his characteristics were more or less torn out and given to everyone else. But also, the wealthier individuals, who had control over Greek society and by extension religion, didn't like that his was a death cult that practiced human sacrifice.