I think quality coaching and community support are the two biggest factors. It's all in what is valued by a particular community. Obviously, Grundy and Christiansburg put a ton of emphasis on their wrestling programs, so those schools' wrestling teams always excel. Here's a mind-blower: since 1986, there has been exactly one year when neither the Golden Wave nor the Blue Demons won a state title on the mats. Yet, most of the rest of the sports at Grundy and C'burg are usually nothing to write home about, with the notable exception of the Motley era in C'burg.
Here in Salem, football is king. If other sports do well here and there, the general reaction seems to be, "Oh, that's nice." But football must succeed. So, while the overall level of athletic success across all Spartan teams would probably not be among the top ten or fifteen schools in 4A year-to-year, football is usually a serious contender.