Punishment
After his 'failure' of summoning 375 Silverfangs instead of proper Legendary Summons, Michael paid more attention to the Named Summoning Scrolls. At least he could tell what he would summon with these scrolls. That made everything a little bit more simplistic.
He created 2400x 3-Star Named Summoning Scrolls and 15 4-Star Named Scrolls with the remaining Ordinary Summoning Scrolls. Michael had to experiment a little with Insert and Extract to use the remaining Ordinary Summoning Scrolls efficiently until he gave up. Multiple highly efficient ways existed, yet finding the perfect one was too difficult because some factors were luck-based. Michael couldn't logically pinpoint luck-based factors. To be precise, he didn't think it would be worth the effort.
He obtained 100,000,000 Ordinary Summoning Scrolls every few months either way. It was the Valyr's payment for acquiring the Savannah Region from him. Therefore, Michael obtained them for free – basically.