It is clear that this design is heavy, weakens the structural integrity of what was once a simple diamond frame, introduces bushes that wear, does the 'pedal bob' and complicates the maintenance. However, what is in it for the manufacturer?
'Horst Link' and other properly thought out suspension designs are patented, these patents cost money to licence, whereas the design discussed here is royalty free. It costs nothing apart from a few lumps of ugly metal.
Not wishing to defend the design, however, it does have some benefits with 24 and 20 inch wheel children's bikes, providing a lower standover height and providing some protection for the back wheel from kerbs and other objects 'in the playground'.
From a retailers perspective the differential between the non suspended and cheap suspended variant can be all of £10, which is £10 more in the till. The customer gets 'full suspension' for all of £10, which can be sold as a 'bargain'...