Although the L type (∼70%) is more prevalent than the S type (∼30%), the S type was found to be the ancestral version. Whereas the L type was more prevalent in the early stages of the outbreak in Wuhan, the frequency of the L type decreased after early January 2020. Human intervention may have placed more severe selective pressure on the L type, which might be more aggressive and spread more quickly. On the other hand, the S type, which is evolutionarily older and less aggressive, might have increased in relative frequency due to relatively weaker selective pressure.
It's too early to really know for sure, but one thing that often happens with viruses is that over time, the less fatal versions spread more effectively. It might be that the L type is the more lethal type which killed so many people in Wuhan, and the S type is the more silent type that is spreading around the world with a lower mortality rate.
Probably just wishful thinking on my part, but it's interesting to be aware of the possibility.