Apart from design differences, the TIC-80 is free and open source. PICO-8 is not. This could mean that whatever you create in the PICO-8 will be playable only as long as the owner of the platform is interested. Whatever you create in the TIC-80 can continue to be playable even after the original developer loses interest in the project. There is a healthy community around the TIC-80 that cares about the continuous development of the platform. There is an open atmosphere around it. Anyone can be a developer in the TIC-80. Students don't need to ask mom to buy a license for them. On the opposite, PICO-8 feels like a walled garden. This was the main reason I chose to develop my tiny games in the TIC-80.