Up until 2 years ago I couldn’t either (still never orgasmed from Oral ever). My masturbation method was jumping (actually only 10% or so guys do this I found out and it causes some issue).
The reason was trauma related, but don’t worry. Practice makes perfect. I started by using some toys to help try to learn how to do it.
So talk to him, practice, and there are fun toys you can play with too.
Not all guys do the death grip, and it is a myth since men and women don’t talk very well so ladies have to assume and presume.