It was in the tradition of ancient people to name the stars and planets after their gods and goddesses; the Roman Empire lasted the longest and was the most well remembered and modern people have continued naming planets, moons, and stars after ancient deities.
As to why Pluto/Hades specifically... Pluto is a cold, dreary place, and in Greco-Roman mythology the underworld was similarly cold and gloomy. Also, Jupiter, Neptune and Pluto were regarded by the Romans as a bit of a troika; Zeus ruled the air, Neptune the sea, and Pluto the Earth (as in the underground part of it). Pluto was therefore one of the most prominent/prestigious Roman gods not to already have a planet or other celestial object named for him.
The dwarf planet, Pluto, was named for the Greek God of the underworld.
The formal designation of Pluto now includes a numerical prefix, but it has received little use. It is "134340 Pluto".
Pluto the planet was named after the Roman god of the underworld, not the Disney dog. The name was proposed by Venetia Burney, an 11-year-old schoolgirl from England, in 1930. Pluto the Disney dog was named after the planet, not the other way around.
Plutonium
The dwarf planet Pluto was named after the Roman god of the underworld.
Named for Pluto, ancient god of the underworld.
Mickey Mouse had a dog named Pluto.
The dwarf planet, Pluto, was named for the Greek God of the underworld.
the Roman god of death Pluto
The planet with a moon named Charon is Pluto. Charon is the largest of Pluto's five moons and it is about half the size of Pluto itself.
Pluto is named after the roman name for the greek god Hades.
Pluto got named by Percival Lowell
Pluto. Is Pluto a planet these days?
Pluto is the Roman version of Hades
The formal designation of Pluto now includes a numerical prefix, but it has received little use. It is "134340 Pluto".
Probably Plutonium but I do not think it is named after Pluto.
Pluto the planet was named after the Roman god of the underworld, not the Disney dog. The name was proposed by Venetia Burney, an 11-year-old schoolgirl from England, in 1930. Pluto the Disney dog was named after the planet, not the other way around.