Volkov's style works because he can rely on the referee to stand him up, and he's automatically stood up at the end of the round.
The Werdum fight was very similar. Werdum took him down, and Volkov just held onto closed guard. Werdum gassed himself out trying to finish Volkov, and Volkov finished him in round 4.
That's not entirely true...
In first round, Werdum was standing over him, Volkov got a hold of his ankle, tripped him and was able to stand up.
In second round, he had to ride out the round defending on the bottom indeed.
In the third, he managed to scramble up and escape while Werdum was passing his guard.
Then he successfully defended arm bar, and shook Werdum away from himself.
He also'd started to successfully defend TDs/top position in the 3rd.
Against Blades, he was up against way heavier, younger, stronger wrestler.
Both were very cautious, Blaydes offensive was methodical, while Volkov was pretty much purely defensive, didn't want to get punched, so was just sitting there, holding on Blaydes.
Stalemates will happen in fights like that... If Blaydes was trying some dynamic armbars, like Werdum, Volkov would have a chance to escape too.