Why did the Ascians never try to do these?

[Anonymoose]

See, I always thought he didn't recognize Azem's soul before the very last moment.

If it helps, my interpretation is rooted in Hythlodaeus, who can tell on-sight that we were Azem and speculates that Emet-Selch did, too.

Hythlodaeus
A hue that distinctive cannot be mistaken, no matter how thin the soul is spread. Hah! This is just the kind of fate I might expect for one such as [them]. Surely Emet-Selch has recognized the hint of “[them]” in you...?