Just to get pedantic for a second (it’s practically my default state after all 
), the issue is one of hydration. It’s not that dry food seems to necessarily cause the development of more struvite crystals. It’s that wet food adds more moisture to the diet that dilutes the urine and makes the crystals easier to flush out. Particularly since domestic cats were developed primarily from an arid-adapted subspecies of wild cat - the wild animals got a lot of their water demand from live prey. Consequently it seems many domestic cats don’t like to drink a lot from their water bowls. Hence the development of fountains and such to entice them - moving water seems to encourage at least some individuals to drink more.
Boys are more susceptible than girls because of anatomical differences. As a vet described it to me, if female urethras are like straws, male urethras are like coffee stirrers. Much easier to stop up. One drastic surgical treatments it to make the male opening a lot larger. There also seems to be a possible genetic factor in crystal formation (Siamese seem more prone for whatever reason).
The prescription diets are pH corrected and/or low in magnesium and phosphorus, all of which seem to be loosely correlated with struvite formation. However they aren’t exactly premium foods nutrient-wise and they aren’t always super-palatable to picky cats.
After one of my two young male cats got a urinary blockage at an adolescent age (Sunday, emergency vet - very expensive), I switched to a mixed dry/wet prescription diet which both my cats were a PItA about eating. After he got a second blockage several months later (again Sunday, another emergency vet - even more expensive 
), I switched to an all wet diet, tossed the prescription food for premium canned and he never had another reoccurrence until he passed ~14-15 years later from an unrelated genetic heart issue.
Always good to keep in mind that old water/wastewater treatment adage: The solution to pollution is dilution.