It's only large capital expenditures (that usually can be resold for similar amounts as purchased at) that require amortization/depreciation. For example, an Excavator.
Same if you build a house, building, etc. you can expense the labor that went into it that year, as well as materials consumed in building in. [https://onekeyresources.milwaukeetool.com/en/when-to-expense...]
There are situations the labor would be considered a capital expenditure, which you can then get ROI off of, but amortizing labor costs over multiple years is a pretty odd situation.
If you couldn't, it would get reaaaaly ugly real fast, since the big challenge here is that cash gets spent this year, while it is only deductable against income taxes years later. So if I get $1mln in income now, and spend $1mln on say software R&D, i'd end up owing a bunch of taxes on the $1mln of income using cash I just don't have anymore.
In the case of an excavator or whatever, there is a sellable asset which someone can turn around and sell to get cash if there is a problem. In the case of construction labor, there is usually some improved property or accounts receivable somewhere that can be used to pay the taxes too. In software R&D there rarely is.
Outsourcing can do it though.