Get used to it!
For the last few years there has been a "Summer No Low Fare Zone". As long as they are able to fill planes under the "halo" of infrequent flyers perception of low fares that will not change. The most likely challenger to unseat Southwest is Frontier. Their in flight product is not significantly inferior to Southwest's.
I abandoned Southwest for Frontier in the latter half of 2015. I saved a few thousand dollars and was anticipating becoming a loyal Frontier customer. Unfortunately Frontier's achellilles heal is their tendancy to premptorilty cancel new routes before they have a chance to mature.