The effect of cheap money on Bitcoin is a second-order effect whereby people have access to money they wouldn't otherwise have, due to additional debt. It's similar to the effect witnessed during the run-up to the 2008 meltdown where people were refinancing their homes and cashing out (on-paper) equity to use for propping up their lifestyle or buying more real estate.

The point is that it is impossible to separate Bitcoin and it's fate from the greater economy. Cheap money fuels bubbles. Last time it was real estate, this time it looks like Bitcoin.