I've lived in several states where frontage roads are common (under various names), and Texas was the place where they were most plentiful.
Older interchanges tended to run the frontage roads below grade to make them cheaper. But more recent ones tend to keep everything above grade due to flooding.
Or is it just that Texas has one famous one and people extrapolate that to mean the whole state is absolutely smothered in interchanges
Texas has a crazy number of highway interchanges. This is a partial selection of highway interchanges with frontage roads just in Houston. There are probably a hundred more across the state:
https://maps.apple.com/?ll=29.874104,-95.556634
https://maps.apple.com/?ll=29.726083,-95.459588
https://maps.apple.com/?ll=29.784165,-95.561947
https://maps.apple.com/?ll=29.785693,-95.777690
https://maps.apple.com/?ll=29.771646,-95.154931
https://maps.apple.com/?ll=29.940698,-95.293735
https://maps.apple.com/?ll=30.128100,-95.229756