Why don't F1 cars run on Friday at Monaco?

You are correct in your assumption. Historically, the race track was opened to general public vehicles on Friday. However as time passed, the viewership and the revenue from Monaco dropped. read more

There are a number of different reasons to why the F1 cars don’t run on Friday in Monaco during the race weekend: First off, it is so that the inhabitants can get a pause from the chaos that takes place during the F1 when the whole city is shut down and it gets almost impossible to get around the city. read more

I just read that there won't be a Friday practice, there will be one on thursday. To be honest I don't remember if it always happens like that, on a thursday. read more