I've been through several network upgrades. You are saying the fiber in the ground lasts a long time, but all the equipment on either end gets replaced every ~5 years. I agree this build out seems pretty crazy, but people were saying the same thing with the internet. Arguing if the equipment has a replacement rate of 2-6 years or 30-40 years, I think isn't the part that makes this a bubble.

For fiber, the main costs were not the fiber itself, but acquiring the rights to lay the fiber and the labor to do so. The equipment at either end has a lifespan of somewhat less that 50 years, but that's a minor cost.

Conversely, for the data centers we're talking about, the cost of the things that need replacing every five years is one of the primary costs.