It's a good suggestion, and it has been made before (in the Site Issues forum). The problem is that there are 20,908 topics in the General Forum, some of which are breast expansion content, some of which are big breast content, but many of which are combinations of the two. Even if there were a clear-cut delimiter for deciding which combination threads should go in which category, we simply aren't staffed for a sorting job that big.
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gonZo