Don't Mess with Texas
This picture sums up why I hate movies and TV shows about Texas.
Only Yankees and eastern liberals (not much difference between 'em, really) would wear knee-high cowboy boots like this (I've never seen boots that tall, not cowboy boots). You put the pants over the boot for one very simple reason: wherever you are walking, whatever you are walking through (especially grass taller than cut St. Augustine, which you won't find on a Texas ranch), seeds and burrs (and Texas has lots of sticker burrs of one kind and another) and just plain old dirt will quickly settle to the bottom of your boot.
Women might wear their boots "out" like this, for a dance or any occasion that doesn't involve walking on any surface not man-made, but any fool who drove around dusty Texas, or walked through a Texas field of any description, would put his pants over his boots as soon as he could.
Or go to town and buy some pants loose enough to go over his boots. No one in Texas wearing boots would wear jeans that fit like tights, either.
And what's that guy behind the wheel wearing? English riding boots?