While lightning is open to anyone it's still a complex setup. The tools are getting amazing though!
Both the Voltage API for businesses and Alby Hub have made huge strides to make setting up a lightning experience easy.

Secondly, merchants are terrified of Bitcoin's volatility. So, the introduction of stablecoin liquidity via Taproot Assets will be massive to broader adoption. If we make lightning into a protocol for instant payments instead of "spending your bitcoin", we'll take away the friction to moving value over Bitcoin infrastructure.