Why are stalker talents only usable once per encounter?

[Ravingdork]

From the Stalker Talents general rules:
A stalker vigilante can apply only one talent marked with an asterisk (*) to a given hidden strike, and only when that hidden strike is dealt against a foe that is unaware of the stalker vigilante (or who considers him an ally), unless otherwise noted.

With a few exceptions and corner cases, many of the stalker's talents can only be used when a foe is unaware--essentially only ever at the start of the fight.

Why? What purpose does such a limitation serve? Why not have them work on any hidden strike?

Seems like the more I read it the more arbitrary limitations I find in the class.

[Milo v3]

Well, you could stealth after attacking to do it again.

[Rynjin]

Yeah. If only any of them were good enough to limit you to a Standard every round.

[Imbicatus]

Does Up Close and Personal's "This attack applies the stalker vigilante’s hidden strike damage as if the foe was unaware of the stalker vigilante." Allow you to apply talents as if the foe was unaware as well?