Wonder if there's something like a "critical mass" or another factor in the transmission equation that has to be met before it takes off like that.
In a way, we have seen similar things before - Germany, Greece, and Portugal for example didn't have much of a first wave. We thought they must have done a good job in containing the virus, but whatever they did then, didn't help them much when the second wave hit. On the other hand, Italy had a devastating first wave - we thought it was because nobody knew what was hapening, but in a way it is still surprising because they must have started with very few cases. Maybe there is something extra we could see in the modelling.