Because its darkscape - nowhere is safe.
They dont want people to be able to dive into their poh to escape danger so portals cant be locked and you get thrown out of build mode if someone enters.
you cant enter your poh unless out of combat i believe, unless they changed that, so there is no point in having it as a hide away, plus with higher level construction there would be portals to teleport
@ ghostpeople -- What you should really be asking is "How the heck did they find my poh in the first place?", at least in my honest, personal opinion.
~D. V. "It might explain a lot..." Devnull
and they followed me when i was getting lvls in taverley,