Because Lightning is (realistically) ONLY usable in a custodial manner, and because no vendors want to deal with Bitcoin's volatility. Businesses will soon be adopting USDC bacause of it's financial advantages over tradfi and because they are familiar with the dollar, AND (unlike Bitcoin) because it is rapidly being sanctioned by the US government (genius / clarity). So the flow will be Monero to USDC (or perhaps Zano's USDCx). But lightning is a massive, complicated, centralized fail that is only being supported by Bitcoin capture fiends like the Jack off twins, Dorsey & Mallers.

Nosmero