Why are Bok globules so cold?
Most of my information is sourced from here:
https://apod.nasa.gov/apod/ap990511.html

To summarize the source, Bok globules are extremely cold because of their composition -- they're generally just clouds of pre-stellar material which block out all light. This makes the interior of Bok globules "shielded" from interstellar radiation that would otherwise heat them up.

Also, you claim that the globules should have retained some heat from gravitational collapse. However, since the globules don't encounter much friction in space, and there aren't many major collisions that produce changes in kinetic energy, there isn't much energy to dissipate. After all, even Bok globules aren't dense objects by any stretch of the imagination.