The problem is that this is a truly regional event and not just isolated to Texas. The entire central US is struggling right now. The SPP (which manages electricity for Oklahoma, Nebraska, Arkansas, and other states) has been struggling with forced blackouts over the last several days as well. They don’t have enough power for their own grid, let alone enough to share with Texas.
If Texas was more interconnected with the SPP, the end result wouldn’t be Texans all having their problems solved. Many Texans would still be without power, but so would many more Oklahomans. The fact that the Texas grid is separate is the only thing keeping OK from having even worse blackouts. Which makes sense, because the entire point of grid isolation is to keep issues localized and not cascade over the entire network. And that’s working to Oklahoma’s benefit right now, but Texas is getting the short end of the stick.