Why Hulk (Immortal) didn't regen?

I was fight Hulk (Immortal) in Cavalier with Namor and was expecting him to regen when I got him down to 1%, but it never happened and he just died.
Why ideas why? Does DOT stop the regen?
https://youtu.be/XuNRTCiV6_Y
Why ideas why? Does DOT stop the regen?

2
Comments
As it says in his Spotlight: when Immortal Hulk would receive any damage that would knock him out, consume 15% Max Health as Gamma Radiation and receive an Immortality passive
for this fight his DOT is killing him faster than he can gain stacks of rage !!!
They messed up with this hulk. The community is obliterating the mechanics