As a member of our local planning commission, our local ordinances do require a new cell antenna (or any other antenna that we regulate) to offer co-location for a minimum of one additional user of the same type on the structure. Most cell towers that have been installed here offer locations for two users, with some offering three locations. Typically the builder / prime user gets the top location on the tower, and follow ons get the inferior ones.
We also require the applicants provide engineering studies demonstrating there is no suitable existing location within a mile radius to encourage co-location. In our community, that has resulted in one location with two cell towers within a few hundred feet of each other. The existing tower built for previous generations was not tall enough to support 5G operations in the co-located spot lower on the tower.
When cell towers were new, we had full houses for planning commission meetings opposing their location. The last ones we have done in recent years have had no public input - the public has generally decided the utility of the service is the more important factor.