This is not just a problem with tax law, but any law. The problem with the spirit of the law is that it means different things to different people. Both intent (and morality!) differs greatly between various people. Hence we stick to the letter of the law. A simple example:

- Let's say one can do A, B, C and D. They all represent similar situations.

- For some reason, the government wants to block the above.

- They create a new law, blocking A, B and C. They forgot D.

Now, they might have wanted to block D as well. But how do you know? What if D gives you a significant advantage over competitors?

One thing I've noticed, hanging out with lawyers, is that governments often make a lot of half assed laws. Closing the "loopholes" isn't hard - it just takes time + requires proper work. Also, don't forget, some loopholes are there by design.