Well yeah, in practice we don't have Turing Machines with infinite bands, but finite memory, so the number of states is bounded. The number of possible inputs

Well yeah, in practice we don't have Turing Machines with infinite bands, but finite memory, so the number of states is bounded. The number of possible inputs and states for even a moderately complex program is also so astronomically high that it quickly far surpasses the number of atoms that earth consists of, so, yeah, "cost reasons" is one way to put it. We also don't transform sheet rock into gold for "energy reasons".