It's likely due to some other factor or individual difference. To my knowledge, there is no evidence that stimulants affect people with ADHD any differently than people without ADHD. By differently, I mean having a paradoxical reaction that can only be attributed to having ADHD.
Correlation does not imply causation, but people still try it all the time.
More importantly, the dose of desoxyn (methamphetamine) used therapeutically for ADHD is *much* lower than what's consumed recreationally. That's really it. Use low doses, as prescribed, and the risks are minimal/comparable to most alternative stimulants.
It's like asking why a society where everyone has cups of tea twice a day has a different relationship to caffeine than a frat house where they're drinking 3 cans of Red Bull a night.