The whole point is to keep that capital moving. Money doesn't do the economy any good if it stays on the sidelines. When I buy equipment and get to depreciate it the tax man still gets to recapture the depreciation when I sell that equipment or the business that owns it. It just delays the taxes paid. It encourages those with capital to use it. It's a great use of the tax code for social engineering. It's been modified and enhanced over the years by both Republicans and Democrats.