I agree that that isn't a good argument.
A better argument is that this is how the government gets a sense for what the population is. For example, a growing percentage of "non-religious" or (to a lesser extent) non-Christian religious makes it harder for the government to continue justifying subsidies for religious schools and special status for religious organisations. A higher percentage of people saying they travel to work by bike or public transport helps justify increasing funding for those methods over continued motornormativity.