Texas is connected to the Eastern and Mexican grids and can share power through high voltage DC interconnect stations. They simply don't sync to the phase of other grids.

Other states/feds were happy to take the "free market" of Texas during WWII when they direly needed it and other Gulf states begged Texas to connect.

It's a holier than thou thing for the other states. "Free market" buying from Texas when they need it, when they don't it's "fuck the free market" and cut texas off via legislation and refuse to provide the same assistance that Texans provided.