JPMorgan thinks the bitcoin rally is unsustainable and doesn't make much sense

A visual representation of digital currencies.
Yuriko Nakao | Getty Images

It seems there aren't enough buyers to keep bitcoin at record highs, according to a new note from JPMorgan.

Bitcoin set another record high on Wednesday above $51,000, pushing the cryptocurrency's year-to-date gains to nearly 80%. The rally in recent weeks is an extension of an even more dramatic run that dates back to last October.