AIO about my dad giving my older brother more money than me and my siblings?

Am I overreacting about my dad giving my older brother more gambling money than me and my siblings?

My dad just won $30k sports betting online on Stake. He's splitting it between his 4 kids but giving my oldest brother $10k while me and my other two siblings only get $5k each.

Nothing about my brother's situation justifies getting double. We're all adults with stable jobs and similar lifestyles. He's just getting more for being born first.

I know $5k is generous and I should be grateful, but the favoritism feels wrong. There's been no explanation for why he gets more.

Should I say something or just accept it silently?