Because they are tapping into a market that they know is present and ready to throw away money in the pursuit of speed development for their kids. The same goes for coaches without much useful training knowledge and their athletes.
Most parents and many coaches (at times one in the same) can’t discern between a good program and a bad one and come to the belief that it must be gadgets and gimmicks that produce results. Nike knows that people are going to spend money on the gadgets so why not take their cut out of that that market that is so willing to spend their money.
The parent or coach not knowing any better sees fancy gadgets, pulleys etc. and they can’t see what knowledge or experience another coach might possess so they go with they can see- fancy toys.