Because they thought it was infringing on their freedom when told to wear masks and social distance

They tried to avoid the plague like the plague,
but they couldn't flee the fleas

They did. Your confusion is on the meaning of the commonly used phrase.

Avoid it like the plague actually means you’re going to do almost nothing but hope you don’t die.

Did you not witness the stupid during Covid ?

You can watch a very historically accurate and 100% true documentary on netflix: The Decameron

You see, the phrase didn't exist at the time, so they didn't know they had to avoid it

They thought the plague never avoided anyone, so why should they?

Well, they were rubbing shit into their open wounds so you tell me.

Is this evil jonkler cart reference?