I guess the short answer would be that what is crucially important to productivity growth is real business investment in new machinery and equipment, as well as in skills. The link from a general corporate tax cut to higher levels of real corporate investment is fairly tenuous.
If you take the energy sector, for example, parts of the resource sector are doing very well, and are very profitable. They are investing. Just a cut in the corporate tax rate makes no real difference to their investment rate. When companies are struggling, often the corporate tax rate is irrelevant to the real investment decisions.
A lot of the manufacturers that are now going out of business because they're not earning profits or are very close to losing money just don't benefit from that measure. I think a much more effective way to spend money that would go on a general corporate tax cut would be to take much more targeted measures.