You don't have to take every beloved childhood character and explore their origins. Nobody goes, "Gee, that Very Hungry Caterpillar sure is hungry. How did he get so hungry? What childhood trauma caused him to be so hungry? What were his decisions leading up to his current state of being very, very hungry?" No. He's hungry, and he's a caterpillar. I'm okay with that. I'm satisfied.
Also, you Hollywood assholes already tried this. Remember that 2005 version of Charlie And The Chocolate Factory, in which Johnny Depp pretended to be a sex offender? Remember how you gave him a tragic past of having a dentist for a father who never let him eat candy, as if we somehow questioned why someone might end up really liking candy, a food so delicious that even stupid ants like it? Do you remember how much we hated you for that? Do you think we're too dumb to notice you doing it again? Are you a bunch of predatory worm creatures in harvested human skin suits trying to baffle us into extinction? Well, are you?
By making Wonka's backstory, you're basically heading into The Grinch territory. And that was a movie that made Dr. Seuss spin so fast in his grave that he's become an gyroscopically immovable force. "Why is the Grinch so grinchy?" nobody asked. Hollywood answered, "Because he was teased in school." Oh gee, thanks. Thanks for clearing that up. I couldn't possibly use my imagination to conjure reasons for someone to grow up to be grouchy. No, I couldn't focus on the movie until that burning question was answered. When Dr. Seuss originally introduced the Grinch without explanation, I screamed, "WHY, THOUGH? WHY IS HE SUCH A GRINCH? WILL NO ONE EXPLAIN THIS TO ME? MUST I GO TO MY DEATH WITHOUT EVER KNOWING HOW THE GRINCH BECAME SUCH A GRINCH?" I'm kidding. I did none of that, because I'm not a total moron. God.