This is a myth, created so cloud providers can sell more, and so those who overpay can feel better. I've been using dedicated servers since 2005, so for 20 years across different providers. I have machines at these providers with 1000-1300 days of uptime.
You did not say what system you use on them, but don't you need to reboot them to apply kernel upgrades, for instance?
I run most of the workloads in containers, but there are also some VMs (mostly Windows) and some workloads use Firecracker micro vms in containers. A small number of machines are rebooted more often because they occasionally need new kernel features, and their workloads aren't VM friendly, so they run on bare metal.