Don’t get me wrong - performing high rep deadlifts at speed is certainly not ideal for learning and encouraging solid deadlift technique. However, and for example, if you’re doing fifty deadlift reps for time, you may tend to become rather efficient (again, consciously or subconsciously) at lowering the bar simply because you’re trying to conserve energy.
In other words, you’re letting gravity do all the work of lowering the bar, and herein lies the key.
The Solution
Gravity likes to pull things down in a straight, vertical line, which is exactly the bar path you want when setting the deadlift down. You’re not going to drop the bar, of course, but one of your main tasks when setting it down is to simply stay out of the barbell’s way.