Maybe it's how much of an interesting character he was?
With Nicholai, I think he could really shine, if given another role.
I don't know if you've played Outbreak, but in the epilogue, there is a scene where it shows the fallout from the nuclear explosion, and what's left of Raccoon, and it shows a couple of researchers stationed in there, and one of them talks to somebody from Umbrella on the phone. Anyway, the guy on the phone sounds just like Nicholai, I'm sure it was the same guy who voiced him in Outbreak, and maybe even the character too. Either way, it would be nice to see him at least once more.