Because it's not about the lifetime of the person creating the software, it's about the lifetime of the software created during employment. The created asset can be used indefinitely after the employee has left. The salary is now considered the capital investment to create the asset.
At least that's now how the IRS sees it. Similar to buying machines to create a physical product.
Maybe they read all these articles about developers working in a feature factory.
The IRS should do a code review and see. That script you wrote at 3:00AM after waking up to your pager? That thing is going to be around forever and will have to be amortized over the next 2000 years. 5 years, you're getting off easy ;)
I expect that there will be some sort of code reviews by software experts in the future during a large scale tax audit. Because there is a distinction between regular software maintenance (including diagnosing and debugging) and an actual upgrade or enhancement. So it's not like you just capitalize 100% of the salary, unless it is clearly a support role. But even for testing and quality control, they make a distinction between before and after putting the software into service.
For most small and medium businesses (certainly not FANG), you wouldn't amortize the cost of said server but would take it as a Section 179 expense. This would allow the business to expense the full-cost of the server in the year it's placed into service. Section 174 just further commoditizes the software development skill. Question is: can software dev labor costs be expensed via the Section 179 rule, up to the limit (somewhere north of $1.1MM).
TFA gives an example of amortizing the cost of a $2,000 server with a 4 year life. If you did not amortize the cost, you would have a "bumpy" expense with a $2,000 charge in Year 1, then $0 for the next 3 years. It is more convenient to smooth out the cost of the server over the expected lifetime, instead treating it as a $500 cost in each of the 4 years' of its expected life. Essentially treating it more like a service or pay-over-time situation.
But employees don't work like that. Employees don't have multi-year expected lifetimes which you are required to pay for upfront. In the US at least, it is fairer to say that an employee has a 2 week expected "lifetime". If you stop paying them, they will go somewhere else.
How can you take something that you essentially lease 2 weeks at a time, and amortize it over 5 years?