Different times, different principles.
Back in the 1840s, Texas realized they couldn't defend their borders with 19th Century technoclogy so they joined the Union as a way to protect itself from invaders.
They were tag-alongs in the secession movement of the Civil War which was led by other Souther states.
In today's times, Texas has the resources and the willpower to go it alone without Washington's help or influence. They can better control their borders than apparently Washington will or can, and they need to get out as soon as they can or get sucked under the massive debt run up by the Feds.
Imagine a new country with its own capitalist economy, no I.R.S., respect for God and the ability to learn from the mistakes America has made in the past 200 years. Texas can make it happen.
On top of which, last time the North had all the industry, all the wealth, and all the manpower.
If it comes down to it, let’s see, shall we?
Texas has all the industry - the opposition has none.
Texas has all the remaining wealth - the opposition has none.
Texas makes many, many guns and nuclear weapons - the opposition makes less and none, respectively.
Texas has lots of willing and eager manpower - the opposition has little manpower willing to fight a country that simply wishes to leave.
I like our odds.
Also, right before the end of the last Civil War, the only one of the Confederate States that hadn’t been overrun was Texas. The Union came to Texas and did not enjoy their reception.
“In today’s times, Texas has the resources and the willpower to go it alone without Washington’s help or influence”
Other differences: Texas is now heavily populated, and have had four US Presidents since the war between the states.(that is 4 out of the last ten presidents)