In the stable state, both situations (immediate writeoff vs. amortization) would indeed be identical (assuming constant salary expenses over time).

The problem is that, when switching from the immediate writeoff regime to the amortization regime, you do not have a backlog of past-year expenses that are in the process of being amortized, so there is a sudden jump from being able to write off 100% of relevant expenses to only 20% of them.

Given that shareholders are notoriously interested in short-term profits, hitting profit targets requires either expanding revenue or slashing expenses.