The growth rate lately has been about .5% per year, and the population actually shrunk in the 1980's. [1]
The weather sucks there. It's cold as fuck in the winter, and hot and humid as fuck in the summer. There's maybe 4 enjoyable weeks the entire year.
The politics suck. Steve King is a US Rep from Iowa. For whatever reason Iowa keeps electing him in, and it's embarrassing.
The jobs there suck. Des Moines is a small town, and other cities are even smaller. There just aren't enough tech jobs to keep ISU and Iowa graduates in the state. The best and brightest leave.
Yes, Google has a data center, but it's in Council Bluffs. Have you ever even heard of Council Bluffs before that?