You nailed it right there - 10 edges might be most important, and others you take just because it's fun, not because they empower you.

So if those extra edges don't make a difference, why take them away?

Taking your example with bards, Allysia and Salyeris probably had different edges and tried different things. Isn't it nice to have customization options? Some edges could be taken (or not taken) for RP purposes even.

Now whenever you feel like rolling another bard, your points will be spent on essentials, reducing the customizability value. You won't have those 10-15 extra, those that "don't matter" but for some reason still need to be taken out.

Yes, edges are mostly convenience. But I like convenience, dammit!
Again, why can't we have nice things?