I don't really understand corporate taxation, but maybe someone here can educate me. Why do we expect cutting corporate taxes to increase investment? Aren't co

I don't really understand corporate taxation, but maybe someone here can educate me. Why do we expect cutting corporate taxes to increase investment? Aren't costs associated with infrastructure, hiring, wages, etc. considered deductible business expenses? I suppose there are some edge cases there like payroll taxes, but it seems like most of what a corporation spends money on is effectively coming from pre-tax dollars.