Why I'm still not replacing my NAS HDDs with SSDs

Deciding between SSDs and HDDs for your network-attached storage (NAS) can prove challenging if you're just starting out or are looking to do some upgrades. I've considered the move from HDDs to SSDs a few times now, but I always come back to the trusty mechanical hard drive. My reasoning involves costs, capacities, performance, and longevity (depending on workload). Here are some that prevent me from making the switch, though I'm sure I will do eventually.