Also I believe the lemon in dishwasher tablets is actually an active ingredient. Rather than just being for the smell, the Limonene in the Lemon actually helps cut through grease and stuck-on stains. It’s also a natural non-toxic insecticide.
I also suspect that makers of lemon juice believe that whilst we may like the taste of lemon, we’d prefer it without all that bitterness. Have you noticed how lemon juice and actual juice from a lemon differ in terms of the bitterness quite significantly?