You don't have to clean them all the time. If have a shop-vac you can do this:
Fill a spray bottle with a very strong solution of plain 'ol laundry detergent. Take the mats out of the car, spray on the soapy solution and let them soak for about 5 minutes. Then take a brush and scrub the heck out of them. Then take a hose and rinse them real good. Then use a shop-vac to suck out the extra moisture and let them air dry. This will take an hour or two to do but it works. My friend does this a few times a year with his '98 Q45t which has a tan interior. He rarely cleans his car in between doing this and the mats still look brand new despite the fact that the car is 6 yrs old.
Or you could buy new mats!
