Why are some apps unmovable?

I recently just started downloading a lot of apps, and sometimes it will come up with saying insufficient storage available even though I've only used 4GB of a 32GB card. I'm not sure how it's not working. So, I tried installing an app that puts apps straight to the SD card, but then it says some apps can't be moved because they are ROM only. It's taking up all the space of my 1GB internal storage, and I can't move them. I really need help.