The only reason I can see for languages to concentrate faster than they diverge would be if we regularly wanted to talk to computers. The need for a universal infoglot could possibly outrace the kids' dialects developing at street level, and diverging from their motherlodes. But it wouldn't be spoken between humans much, and there would very soon be regional differences. Swiitzerteuch (Swiss German) is invariably classed as one language, but there can be so much difference between the versions spoken in adjacent valleys that they use High German or English to communicate between each other.