if you look at the map icon they are now marked with a chevron icon. this means it has a npc core witch is indistructable. only way to take it over is to cheat. you can use gm iv in the console and than you can destroy core. if you are on a server you need to be admin or have been given the ability to use console.
but do not worry, there are outposts out there that are not reclaimed. I think this was dun because it was to easy to find a outpost and salvage the statues and have a cv/base that never uses power to easily.

Thanks Geffin. It makes sense. It is on the starter planet