Some interesting things about the Hogwarts houses
All four have trisyllabic names.
The two houses associated with the "dry" elements - Gryffindor and Hufflepuff - both have ten-letter names, female Heads of House, and founders with bisyllabic first names, and the two houses associated with the "moist" elements - Ravenclaw and Slytherin - both have nine-letter names, male Heads of House, and founders with trisyllabic first names.
The houses associated with "warm/active/masculine" elements - Gryffindor and Ravenclaw - have their dorms in the towers, and the houses associated with the "cold/passive/feminine" elements - Hufflepuff and Slytherin - have their dorms in the basement.
Ravenclaw is the only house with an avian mascot, and Slytherin is the only one with a reptilian mascot.
This is pure headcanon, but I think that at least part of why Slytherin House has never been dissolved* is that the enchantments on Hogwarts include arithmantic calculations that are dependent on the existence of four houses, no more or less, and dissolving one or adding a new one could prove disastrous.
* - Besides all the other reasons, of course.