There are some really retrograde government and bigcorps, running ten year old infrastructure. And if that is your customer-base? You do it. Plus I worked on a consumer launch site for something you might remember, and we got the late requirement for IE7 support, because that's what the executives in Japan had. No customers cared, but yeah it worked in IE7.
Oh, certainly, corporations run ten-year-old software. But for the record, IE 11 turns 13 this year [1]. Which makes it somewhat more surprising to me.
[1] https://en.wikipedia.org/wiki/Internet_Explorer_11