>The other thing is that it’s like, super rare, even rarer than shinies…

To quote Bulbapedia:

Pokérus has a 3 in 65,536 or approximately a 1 in 21,845 chance of being generated on a Pokémon, either wild or bred, effectively making this rarer than a shiny Pokémon, which have a 3 in 24,576, or around 1 in 8,192 chance to be found wild or hatched.

Odds of finding a shiny infected with Pokerus? Worse than winning the lottery. You have a 1 in 178,956,971. The odds of winning the Powerball lottery in the US are roughly 1 in 175,000,000.

The other thing is that it's like, super rare, even rarer than shinies, but when you get it, you can spread it to everyone else in your party and PC box. Don't quote me on this, but I'm pretty sure it's also a good selling point if you want to trade it for a rare pokemon too.