Why are the tax laws so complicated?

Why are the tax laws so complicated?

Why is the tax law so technical? Why can't we have a simple tax where everyone knows how much tax they're going to pay? Why isn't that done? Sadly, it's not done because there's special interest involved. For example, the Savings and Loan banks - and the homeowners - want to have mortgage interest on your residence deductible. Why should your mortgage interest on a residence be deductible whereas, if you don't have a primary residence and you have mortgage interest on some other property, that isn't deductible? It doesn't make any sense. Tax laws are not supposed to make sense and they're not supposed to be fair.