"Traditional accounting depreciation would imply that purchasing local hardware is a terrible financial decision."

Depreciation is designed to _encourage_ purchasing of useful local tools, by incrementally matching fractions of the cost of the tool to the revenue it generates over its useful life. The fact that a graphics card might have a book value of $0 after five years of depreciation is a feature, not a bug.

Since the invention of corporation tax it has also had the benefit of offsetting tax over the same period, instead of just one big offset in the first year.