Differences in network speed between US carriers trace back further than equipment or tower counts. They begin with what each operator bought at auction years earlier.
Spectrum is a licensed and finite input
Radio frequencies are a public resource licensed by the federal government, and using them for commercial mobile service requires holding a license for a specific band and geographic area.
Licenses are awarded primarily through competitive bidding, with proceeds going to the Treasury and terms specifying buildout obligations within set periods.
Because supply is fixed by physics and by existing occupants, an operator cannot manufacture more of the input it needs. It can only acquire what is offered.
Channel width sets the speed ceiling
Data rates scale roughly with how much contiguous spectrum a carrier can devote to a connection, which is why wide mid-band holdings produce the largest gains.
An operator holding narrow, scattered blocks must combine them through carrier aggregation, which recovers some capacity but adds complexity and depends on device support.
Two carriers with identical equipment on the same tower can therefore deliver very different peak speeds simply because of the width each has available.
Clearing incumbents delays usable service
Much of the spectrum auctioned for mobile use was previously assigned to satellite, government or broadcast users who must be relocated or share on a coordinated basis.
Transition timelines run for years, with phased clearing by region, so a license won at auction may not be fully usable for a considerable period afterward.
This is why capacity improvements appear market by market rather than nationally, following the clearing schedule rather than the carrier's own plans.
Buildout requirements shape where it goes first
License terms attach construction milestones, typically requiring service to a defined share of population within a fixed number of years or risk forfeiture.
Meeting a population-based milestone is cheapest in dense areas, so deployment follows the same concentration the requirement measures.
Rural obligations, where they exist, are usually attached to separate funding programs rather than to the auction terms themselves.
Secondary markets move holdings quietly
Licenses can be sold, leased or exchanged with regulatory approval, so a carrier's spectrum position changes between auctions through transactions rather than bidding.
Mergers have historically been the largest such transfers, since the acquiring operator gains a spectrum portfolio alongside the subscriber base.
Following these transfers predicts network performance better than following equipment announcements, because the underlying resource changes hands before any tower does.