Verizon might technically be one company but in reality there are several business units which are actually separate companies in all but name.
When you buy business backhaul from Verizon you get guaranteed bandwidth provisioned on their network from point A to B. They don't over provision because they can't: contractually. If they don't meet their SLA the customer is out of the contract and can go elsewhere.
On the residential side things are very different. We have no SLA other than "pfft whatever we'll roll a truck next Thursday I guess"
Verizon might share long distance backhaul between residential and commercial sides of the company but if so it's done with strict quotas to ensure that the commercial side of things isn't impacted. It's not as though the core network division lets everyone have a free-for-all on the available bandwidth through the core.
If I had to guess I would venture that the consumer group either runs largely or entirely separate equipment. They might share fibers but I'm not all that confident about that. They're very, very close to entirely separate businesses.
