For those who didn't know, Kelvin is already its own measurement. Think of it like on the same level as "meters" or "miles". You wouldn't say "500 degrees Kelvin", like you would 't say "50 amounts of meters".

This is because Kelvin, like meters/miles, are already a measurement of some physical feature, in this case of kinetic energy of the particles.

The word "degrees", on the other hand, does not represent a meaningful measurement of anything. It just means a given part of some arbitrary whole, defined by convention.

e.g. the "whole" of an angular degree is just a single complete rotation. The "whole" of a Celsius degree, I believe is the range that goes between water freezing (0°C) and boiling (100°C) points, and that's why it was also known as the centigrade scale.

Extra curiosity: still as of nowadays, if you say the complete temperature unit in Spanish, you don't say "35 degrees Celsius", you say "35 centigrade degrees" (35 grados centígrados). At least in a colloquial context; not sure how they'd say it in a science-related professional environment.