My opinion on this is that music in explainer videos is like seasoning. Use it appropriately and make the goal to make it unnoticeable.
The upside of using it is that it can mask some of the white noise that you can get in the background in voiceovers. Kind of like sugar masks the taste of medicine lol
Bumpers can be good too - I think - fade in and fade out music is a good way to signal learners - much like the sound and sight of the HBO fizzy screen or the sound of the opening credits of Game of Thrones makes me tingle with excitement (yup, I do love my TV). Bumpers are especially good if you are doing a series of explainer videos.
Another upside is that it helps evoke emotion - tempo and tone can change the mood.
Having said all that - like a good soundtrack - you shouldn't really notice it and a 2 minute explainer video may not need music to hold it own.
I'm curious about what other folks think about this????