Because ice demons have been stealing the cold from the Earth slowly over the past million years. They are very elusive and no one has ever been able to snap a photo, but they're out there. Al Gore tried to tell us about their secret plan, operation G.R.E.E.N.H.O.U.S.E. but nobody listened. So that's why your water is the way it is.
Has the weather been hot lately? Water for a locality is held, often, in a holding tank somewhere close. If the sun shines, it warms up. We've had some hot weather here in California lately, and our cold water is warm enough to shower in - if you like cool showers.
Do you have a water recirculation system installed, if so, the wax valve located under the sink at the farthest location from the hot water heater has failed and you are getting hot water feeding back to the cold water line