I always forget that these things aren't for me. My immediate thought is always immediately "just build your own NAS with a vanilla Linux box and set up Samba or something because then you can make it however you want".
But of course, if I'm someone who knows how to build a NAS and is inclined to do such a thing, then I'm sort of inherently not the kind of person that would be interested in such things and not the audience they're marketing towards, which is obviously fine.
Companies are also much more inclined to spend money to solve a problem while hobbyists are much more likely to get enjoyment out of the process of building. I'm firmly in the latter category, having built a rather robust ZFS array on NixOS with a pretty gnarly NVMe cache hierarchy built on LVM. It was fun to do.
I've been a sysadmin for decades, dealt with *nix based servers since the late 90s, yet for the most part I've used devices like Synology servers, simply because I don't want to have to manage technology to that degree at home.
I've built my own NAS when my last synology died, and I'm not sure I'll build one again. I've dealt with all sorts of issues that I just haven't had to deal with with a packaged solution, and I really just want to not think about that stuff when I'm not working.
Yes, I can absolutely do it for cheaper, better, and with more flexibility myself. Doesn't mean I actually want to.