In my experience most (maybe even all?) of the times I've had to leave a job and I think about how to do so, I end up realizing that the best course is to be honest.

In your position I would pretty much just tell them everything you just said. It's not even close to what I would consider bridge-burning reasons.

What exactly don't you like about saying all those things?

If the reason is along the lines of "because I don't want to", then just say like others have said "I have found an opportunity that I would like to pursue"

Best of luck!