They've been doing this on purpose for years to signal they no longer have their heads up their own asses. The fact that you haven't noticed until now may indicate...
Truth is, you use what browser you like. On my team (MSFT employee) this is a mixture of Chrome, FF, IE, and Edge, based on personal preference.
But like the requisite non-white person in every group photo, Microsoft's choice of browser screenshots most certainly is a conscious decision. For the same reasons. It's not to fake relevancy; it's to signal they're culturally aware.