Fiber buildouts were cancelled back in 2000 because multimode made existing fiber more efficient.

Sorry but that makes no sense in multiple ways.

• First of all single mode fiber provides magnitudes higher capacity than multi mode.

• Secondly the modal patterns depend on the physics of the cable, specifically its core diameter. Single mode fibers has a 9 micrometer core, multi mode 50 or 62.5 micrometers. So you can’t change the light modes on existing fiber.

• Thirdly multi mode fiber existed first, so it couldn’t be the improvement. And single mode fiber was becoming the way forward for long distance transmission in 1982 already, and the first transatlantic cable with it was laid in 1988. So it couldn’t be the improvement of 2000 either.

You must mean something else entirely.