I suspect it is not so much the lack of listeners to classical radio in Texas as much as it is the debt they took on. From what I see, the NPR News Talk format is king and the music based formats are pretty marginal in audience size and revenue. The issue is more about what you pay for the signal than what you put on the frequency. As one earlier post hinted, Classical works in Vermont. It obviously does. It could be getting a little change from the NPR News Talk or the classical side is based more on lower valued frequencies and translators to make it work.
Some say the classical music audience is growing but others say it is dying off. From what I can gather, it is a small but loyal audience. There are many listeners that are occasional listeners. There is even division among those listeners with the occasional more likely to want familiar classical works but is less likely to financially support the station and the core group that demands a wide variety and deep library hosted by people that know and understand the music. Discovery is still important in Classical radio to the point that part of what keeps it fresh to the core group is discovery of works, composers and performances of known works by different orchestras. A host that can tie that all together (ie: studied under X composer and I think you can hear that influence in this work, recently recorded for the first time, performed on period instruments...). Just like other formats, you can be too 'discovery' oriented to attract the occasional listener and you can be too 'familiar' to the point the core listener finds you too bland for their tastes.
Even with that said, Classical radio has changed over the years in just what they will play. You're not likely to hear a lengthy harpsichord work, for example. Classical radio has learned that some forms of classical music are just too much in big doses. Orchestral works and such predominate.
For Public Radio groups that have used the NPR News Talk format in drive times and classical the rest of the day are frequently forced to keep classical alive, mostly via a fulltime station. If a Public Radio group proposes dropping classical, there is usually quite an uproar from supporters who might only be occasional listeners. Public Radio is not really different than commercial radio in that they have to program for the money whether it is via donations and/or Underwriting and grants. Every entity wants to keep costs low should the station have a rough couple of years and anything that is marginal they want to 'go away' because at some point they'll be robbing Peter to pay Paul. The more cash Peter has the better they can stay out of financial trouble. They don't mind having Paul around as long as Peter doesn't become cash poor because of it.