the reason property plant and equipment is amortized over time instead of expensed right away is to match up the tax deduction with the profit. If building a factory and filling it with robots will produce cars over a 10 year period in the future, it makes sense to subtract those costs over the same 10 year period. Matching profits with expenses is essentially why accounting was invented in the first place, so financial statements would show smoother and continuous operation of a smooth and continuous company, instead of big peaks and valleys as if something had happened.

With software companies, developing software (like Microsoft Windows) allows you to profit from that software over the next 5 years. Matching profits with expenses makes rational sense.

Frequenty, politicians use the tax code to implement popular social policy. This way they can reward things and groups they want to, and still be able to say "we aren't giving subsidies, we aren't giving people cash, we are simply giving tax deductions and tax credits" These sorts of programs are, across the board, more distorting of the economy and make the tax code incomprehensibly more complex. But matching expenses against profits? makes perfect sense.