It's not odd; sponsors pick what level they feel they can commit to in terms of marketing support (booth space, banners, etc) and how much internal support they have for the conference or the community (in this case, Python and PyCon).
Microsoft has been an amazing PyCon sponsor for years, and they continue to support the PSF both financially, and by supplying Python core developers with free, unlimited MSDN accounts to help with windows support.
So, don't take a sponsor level as a specific note about how much cash they do, or do not have - a lot goes into a company's choice about sponsorship.
As Jesse stated, it's just one of their many sponsorships, of PyCon, of the PSF, and of the Python developers. Probably their biggest sponsorship of Python is the generous donation of over 20 VS Ultimate MSDN subscriptions which they also let us renew for free, in order to keep up support of Python on Windows. If you do the math on what that'd cost for us to buy on our own, it's a hilariously large number.
Microsoft has been an amazing PyCon sponsor for years, and they continue to support the PSF both financially, and by supplying Python core developers with free, unlimited MSDN accounts to help with windows support.
So, don't take a sponsor level as a specific note about how much cash they do, or do not have - a lot goes into a company's choice about sponsorship.