> I live near Dupont and the bike lanes are super comprehensive, but honestly they seem underused

As stated, there's a larger context. You need good infrastructure so cyclists that aren't the "extremists" will ride bikes. I'd consider myself an "extremist" considering I got an e-bike to commute to Rockville Metro Station when the bus doesn't run.

> genuine question: When a neighborhood is extremely walkable, are bike lanes everywhere necessary?

I'd like to emphasize what the other person stated, that bicycles are for neighborhood to neighborhood travel. In essence, they're replacing trips that would be done with a car.