Microsoft has been telling folks for a while that Microsoft Office 2011 is going to cease getting future development. Lately, they've made it even more explicit that if you upgrade to macOS High Sierra in a few weeks, you're out of luck with Office 2011.
I have received several emails from people worried that this spells doom for Microsoft Office on the Mac. I don't think that is necessarily true. Indeed, without any inside knowledge I’d argue that Microsoft Office is just fine on the Mac. Microsoft is in the software business. They make money selling software and, since they moved Microsoft Office over to a subscription model, I expect they’ve been doing pretty well at it.
When Steve Ballmer left Microsoft, I believe the company took a very big step toward a business model that includes putting its software on all platforms and away from Ballmer's prior strategy of using Microsoft Office to trap people on Microsoft operating systems.
I attend plenty of conferences with lawyers and other fancy people that rely on Microsoft Office on their Mac and they are, by all accounts, signing up for Office365 in droves. I did the same thing. Since subscribing to Microsoft Office365, I've noticed the application has steadily improved with frequent updates. They also put considerable effort into the IOS versions of Microsoft Office.
I think a more likely explanation for the lack of support for Office 2011 in High Sierra is Microsoft's further efforts to push everybody onto their subscription pricing model and devote further engineering resources to the currently shipping version of Microsoft Office, instead of one six years old.