Surprisingly, you got to thank George Bush for that
He made renewable wind and solar energy a major part of his energy policy when he was Govenor of TX. [0].
In 1999, he passed a law mandating Texas to get 2,000 megawatts of electricity from renewable energy by 2009. This helped spurt the entire renewable industry in TX
[0] - https://www.technologyreview.com/2016/08/29/70295/george-w-b...
McGraw Hill was founded by the Bush family before they decamped for Dallas in the 1920s.
You can get around this with DC, and grids do interconnect with DC power, but that requires more expensive equipment.
I tried reading this IEEE article about the time the Eastern and Western Interconnections were connected into a synchronous system (1967-1975) to learn more about the difficulties with scaling interconnections. It mentioned frequency oscillations causing voltage variations close to the East-West connection (p11), which sounds like the issue you're describing. If that is the issue though, then Texas isn't the size limit for a grid because the Eastern and Western grids exist and are far larger.
https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=8594689
A roommate of mine once quipped on something: 'that's like saying my crap smells better than yours'.
Feel free to correct me, I'm not an expert, but Texas runs its own state-only independent grid, it got completely pants in the ice storm a few years ago, and at the time a lot of articles said the Texas grid is fundamentally less resilient that other power companies. Is any of that wrong?
However, Texas is loaded with sun/desert and I believe a ton of wind resources, so it has that going for it for next-generation industry.