Why do my aff dots refresh themselves sometimes?

Classes Warlock
1

Certain mobs my drain soul will refresh the duration of my dots to 100%. Why is this and can we have this permanent

2

As of patch 10.1.5 the PVP talent Rot and Decay now also applies to Shadow Bolt / Drain Soul (it was just Drain Life).
If you’re in Warmode and have that talented, that will be why.

3

Ahhhh didn’t realize. I wish it was just built in.