Why can I access 1 SL soul, but not the others?

Currently I'm able to roll Harbinger on my mage. When I tried to check out the Defiler it wouldn't appear on the list. Why is this?

you aren't trying to check out defiler on a mage are you?

defiler is a cleric soul, only available to the cleric calling

I'm using the correct calling. I can't get a tempest or tech on warrior/rogue either.

I'm not sure (and it would be great if confirmation would come from someone at Trion) but several players I know had made a character using one of the storm legion souls (but not the other 3) and when f2p hit they still had that one character and that allowed the use of that one soul permanently. The other unused storm legion souls weren't unlocked.

If I remember correctly, at a certain point before f2p Trion allowed all old accounts access to storm legion for about a week or two. If those players had never purchased storm legion but made a character with one of the souls, then they kept the access.

Trion said several times that they would NOT take any previous access away from players who had purchased the game at any time in the past.