To put it simply, Big Bank Take Little Bank is a metaphor for the rising capitalist market. According to experts, in a capitalist economy, the rich gain richer and the poor get poorer.
Similarly, the ongoing TikTok trend Bigger Bank Take Small Bank implies that a financially stronger business/bank will eventually take over other firms. The expression, according to the Urban Dictionary, suggests that the individual with more financial resources would eventually obtain control of all assets.