If someone likes a lot of niche stuff and more complex, less accessible music, they are likely to take passion for music more seriously as a hobby than somoene who just listens to chart stuff (not that there's anything wrong with that per-say, but I feel being that level of passive would lead to incompatibility).

Certain genres and scenes are also linked to demographics and lifestyles (e.g. hyperpop being very queer leaning, chiptunes being nerdy, punk being political, bassline and techno being linked to the underground rave scene, etc...)

Also if one of your favourite things is going to gigs and festivals, producing music, or following it, having crossover in taste means being able to share a passion.

A large part of my relationship with my partner is listening to music, either at home on the hi-fi, or at events. If we didn't have a decent amount of crossover, this wouldn't really work.

Having exactly the same taste is probably not so great as I think the differences and gaps are a great space to grow and discover.

Openness to new things? Variety is the spice of life, how spicy are they?