San Antonio is one of those markets along with many others like SLC, Portland, Charlotte, Indianapolis, Nashville, etc. that are simply just not big enough for both the NHL and NBA.
You have to keep this in mind, the NHL and NBA combined play 82 home games. Attendance-wise where do these teams make their money? A good chunk of it is people buying the suites and higher-priced seats. You can't just rely on Joe Smith and his family to buy the $25 or whatever seats all the way up in the rafters and expect it to work long-term. The smaller the market, the less the sports dollar stretches.
I don't know the "merits" of SA as a "Hockey town" (it sucks that they are losing the Rampage but that's another discussion)
There didn't seem to be a lot of interest in Hockey there. Is an NHL franchise in SA a good investment when they'll have the Spurs and Football (not just NFL either) to compete with? Not really.
If the NHL was interested in Texas outside Houston, then Austin would be their city, that is if an owner or group of owners could be found, and also an arena. Frankly it's a no-brainer over San Antonio should the opportunity arise.