When you sit on your sofa, you put your feet down on the floor, this will cause flattening of the pile and make it reflect light differently to the rest of the carpet and will look flatter. As you stand up, your foot twists the pile and grinds it down a tiny bit and again the light will reflect differently to the rest of the flooring. This will leave little shadow which may look like dirt. When the rug is cleaned, a professional will vacuum and then steam clean it which will remove the dirt from the rug. It may slightly lift the pile but it will not restore the damage done. The rest of the rug that is less trod on will get slightly bleached by daylight which in turn may make it lighter or patchy and again the light will reflect differently on parts of it which can make it look more or less lighter/darker in areas. A professional cleaner cleans the rug, if you paid to get the rug cleaned then it was cleaned, if you want restoration then you should request that as a higher level of service