Also, I think many people underestimate how useful strength is in most aspects of life. From picking up groceries, to home improvement projects, to wrangling kids, to getting yourself up off the toilet (a serious problem for older people). Strength makes all of these easier.
I played volleyball recreationally for years and the jumping with arm swing became muscle memory. Last week I was teaching my 10 yo son some volleyball basics and I realized how a few extra movements can impove one's jump (specifically the singing and its timing).
Speed and power is entirely genetic. you're either fast or not. you can either jump high or you can't. you can improve it but only by slim margins.
Strength however, can be trained and improved greatly and well into middle age, which is why barbell training is so popular.
In addition to the skill of jumping, jumping with weight will gain muscle and endurance. It also improves the fast neurologic response that is required for the complex series of movements when changing direction. It also trains specific muscle fibers in ways that aren't in strength training.
Much like squatting, all you have to do to start is to jump a lot. Trainers can point out how to optimize your jump. But a lot of the potential to get high air, land on top of something, or reach something high, is mental.
As he points out, if vertical jump was really trainable, every basketball player in the NBA would have a 48" vertical. But, I assure you, they do not. Only genetic freaks have 48" verticals.