Blade/WMG

In the anime, Blade likes knives so much because of his mother.
In his mother's Death by Origin Story, she makes one last futile stand against Deacon Frost by trying to knife him. Though she only manages to slit his palm,  Furthermore, the knife she used is also seen in the end credits next to a photo of her, which implies that Blade kept it as a last memory of her. His love of blades only grew from there.

In Blade 2, the Blood Pack was intended as cannon fodder from the getgo
They acted like badass vampire warriors, but by and large, seemed to be just elite mooks. What chance would they really have had against Blade? The answer is "none, but they weren't supposed to." Rather, they were supposed to distract and weaken Blade, allowing the vastly more skilled Nyssa and Assad to kill him after the Blood Pack was already dead.

The Daystar virus was either far less effective or less widespread then the Nightstalkers hoped
The first clue to this is that Blade was unaffected, despite the Nightstalkers' fears. Backed up by the monologue at the end of the movie that implies that Blade is still hunting, and the fact that vampires are seen in Blade: The Series.

Blade will become the new father of all vampires, just as Drake predicted
He's far too much of a heroic sociopath to live a normal life, so he starts turning 'bad' people into vampires just for the pleasure of hunting them. Inevitably, a few of these get away, and begin transforming others, effectively 'restarting' the vampire race.

The Strain takes place in the Blade universe
The Master is a Reaper, or perhaps a Reaper prototype that Eli was working on, that escaped the purge, and with the annihilation of the vampire race in Blade Trinity, the Master's bloodline is free to conquer Manhattan. Why they're vulnerable to silver is a question, but it may be an unknown side effect of the Daystar virus, or perhaps be because the Master is simply a flawed prototype. Other vampire ancients include Eli and Drake.