You can't "count every possible program equally". (What probability will you give each possible program? If it's positive then your total probability will be infinite. If it's zero then your total probability will be zero. You can do a lot of probability-like things on a space with infinite total measure, in which case you could give every program equal weight, but that's not generally what one does.)

You can also do probability like things on an infinite space where each finite subset has measure zero.