I actually know a family that does havdala every week with instruments! Okay, I guess they are not typical. For starters, you have to have some talent in the family or it’s not doable.
To answer your question, you have a valid point to some extent, but I guess the point is that most people are not becoming Frum because they want to have Havdala with a guitar. If it’s that important to them, they can learn to play guitar and do this every week.
I assume the point is to get kids interested in Yiddishkeit enough that they will then spend Shabbosim at people’s houses. But I don’t know anything about NCSY, so this would be better answered by someone who does.