[tz] Tzdata for Texas

I have been using tzdata in one form or another for 3 decades and have always been puzzled why Dallas or Houston Texas were never listed as an alias to America/Chicago. Dallas-Fort Worth is currently the 4th largest city in America and Houston is 5th. Is there some particular reason for these omissions? Or is it just that no one ever volunteered to do the work to get them added? Additionally I have never seen El Paso Texas listed even though it is the one spot in Texas that is in the Mountain Time Zone. I know that Chicago has been the Central Time Zone marker as far back as I can remember (at least 1970). Thanks, Ron Sparks