Theres a middle ground ... not everyone who refuses to speak is suffering from social anxiety, or is autistic/AS, etc.. Theres also a lack of making an effort. I used to be very shy, and can still revert to it at times if I don't watch myself, but I try to remind myself to make an effort, to put other people at their ease. I can see that it would be very easy to slip back into my old ways (which ceased thankfully in my early twenties/late teens) if I didn't make that effort.
And yes, small talk is boring for everyone, but the art of conversation is to use it as a sweetener for more interesting topics, failing which you go on your way, happy to have made pleasant social contact with another human being. And yes, you are unlikely to meet the Nobel peace prize or award winning chic lit author at most school gates, but even if you have listened and find the talk genuinely dull, a smile and a "Hello, how are you?" makes you, in many people's minds, a far better person than the one silently judging and trying to get away asap.