Why does the Rambam say all our sages worked to support their studies, yet we have a midrash that’s says Zevulun supported Yissachar’s Torah study?

The rambam in hilchot Talmud Torah 1:9 cites several examples of our sages who worked simple jobs (water Porter, wood chopper, etc) and says that there is no such tradition in Israel where people would ONLY study. Does the rambam not accept the midrash about Zevulun and Yissachar? I know RaShBI would fall under this category as well, but it’s pretty clear from the Gemara that he’s a unique case, so I’ll disregard him, but my question still stands: how do we reconcile the Rambam’s Halacha with the midrash?