There was a car manufacturere in the U.S. years ago by the name of Packard automotive, they made the best cars from a mechanical standpoint and actually sold competitively for a while, they went out of business for one key reason, they couldn't sell enough parts to keep profits up. The cars were a bit pricier than other vehicles but they didn't break as often, so while people were keeping the Chevy's, Fords, etc. for the vehicle's life cycles they were buying replacement parts while Packards were lasting longer and selling few parts in comparison, due to those two factors the company could not sustain a profitable margin. Companies started going to the planned obsolesence model years ago to maintain a minimal demand curve while keeping maximum consumers in the market by offering products with a shorter life cycle.
Should it be illegal? Hell no, as many have pointed out consumers can buy a very expensive product with a very long life cycle and all the amenities, but they aren't prohibited from the market's entry level by prices out of their range, they will spend a mere fraction of what they would spend on the highest end product and get more utility than the actual price. Finally, with the constant improvements and rapid pace of such, consumers actually end up with a superior product for an equal or better price to that which they replaced.