Market Demand Hype drives price
Unlike a normal Draft Booster, a Set Booster is meant to be more exciting to crack open, which is likely why it is popular among folks who just enjoy opening booster packs instead of using them for Limited play (Draft or Sealed)
Circulated freely in booster packs, most official tokens are common - but tokens are distributed in accordance with the frequency of cards that make them
The math is pretty straightforward, but Wizards likes to obfuscate things, because they dont want us to know specifics
Couple that with a growing mana source, and all Zuko asks you to do is exile cards that can be cast during combat
It turns every single creature on the battlefield into target creature you control, legendary or not