The answer to 'carpet cleaning smells bad' is that a persistent bad odor after carpet cleaning is usually caused by trapped moisture or leftover cleaning solution. This can happen if the carpet wasn't properly dried or if the wrong cleaning method was used. The smell may also be due to mold, mildew, or bacteria growth in the carpet fibers.
To fix a smelly carpet, first make sure the carpet is completely dry by using fans or opening windows. You can also try sprinkling baking soda over the carpet, letting it sit for a few hours, then vacuuming it up. If the smell persists, you may need to have the carpet professionally cleaned again or even replaced if there is extensive damage.