You probably meant to say oversubscribing, not overprovisioning.

Oversubscription is expected to a certain degree (this is fundamentally the same concept as "statistical multiplexing"). But even oversubscription in itself is not guaranteed to result in bufferbloat -- appropriate traffic shaping (especially to "encourage" congestion control algorithms to back off sooner) can mitigate a lot of those issues. And, it can be hard to differentiate between bufferbloat at the last mile vs within the ISP's backbone.