You are logging flight time to prove you have experience.

Experience, as in: you have seen complex situations and made the correct choices. You have operated the aircraft safely and not violated clearances, regulations, etc. Taxi time counts as experience, so why shouldn't it be logged?

Cruising along at FL360 with the autopilot on is a place where you could take a quick nap if you were so inclined. With TCAS and ATC radar, the chances of bending metal are miniscule.

Taxiing around Laguardia or O'Hare is not a place where you could take a quick nap. It is a high-threat environment. It's not the flight into JFK that requires experience, it's the taxi in and out. Every trip into a busy airport is a different learning experience, and how do pilots keep track of learning experiences? By logging it.

If taxi time doesn't count as experience worth recording, maybe we need to find a new "deadliest aviation accident in history" since the old one involved aircraft on the ground.