Bloodlust is a built-in catch-up mechanic. The longer a chase runs without the killer landing a hit, the faster the killer moves, in escalating tiers. It resets when the killer hits someone, breaks a pallet, or loses the chase.
Its purpose is to stop a strong loop from being literally infinite. In practice it means a survivor cannot simply hold one tile forever - eventually the killer's accumulated speed will close the gap regardless of how cleanly the loop is being run.
For timed duels bloodlust matters a lot, because it puts a natural ceiling on how long a chase can be stretched by defensive play alone. Past a certain point the survivor has to keep earning time rather than just holding position.