For example, California "only" has 10GW of north-south transmission capacity. TX lost nearly 45GW. Even if it was part of the East or West grid there wouldn't be the transmission capacity there to cover such a loss, plus the states closest to TX which were "connected" were also having major outages, which would have put even more strain on it.
TX does have HVDC interconnects to other states too, but I believe imports to TX were significantly down/zero over this crisis.
TX also has ties with Mexico, but those were useless too because even Mexico was hit hard by this storm and had blackouts all along the US border.
In power grids an interconnector is used to move large amounts of power between grids and if it can't do that then is not an interconnector.
The Texas grid is and independent grid control by ERCOT exactly for this reason.
It was always designed to be independent by the Republican government that has controlled Texas for the last 20 years.
Edit - Texas can only access a tiny fraction of energy reserves due to weak connections to the East and West Grid. Imagine those connections were stronger or direct. I'm sure neighboring states will suffer too. I'm applying general knowledge of distributed systems, I'm not going to act like I know the specifics of the US power grid. If you go it alone, in any system, there are consequences.