I planted eight hollyhocks last year and only five came up this year?

Hollyhocks spread by seeds. I’m guessing some critter got to the roots. In zone 5 holly hocks are annuals. Not pernials. Unless mature seed has dropped, you would not have the 5 you’ve got.

I would call that success!

https://www.burpee.com/gardenadvicecenter/perennials/hollyhock/planting-hollyhock-flowers/article10290.html

Because you live in Michigan, the cold winter could have easily effected their germination.

Hollyhocks are biennials. That means the first year they grow and the second year they flower, and then they are done, unless you are lucky enough to have some seeds that took, which sounds like you did. If you bought plants that were blooming, you bought 2nd year plants. I hope this helps. Good luck!