Perhaps not surprising, Office Insider builds aren’t MSFT Store desktop apps.
I had the MSFT Store version of Office 365 installed in the VM in which I run Windows 10 Insider builds. Then I opted to receive Office Insider builds. That automatically converted Office to installed the old-fashioned, non-Store way. Interesting that given the frequency with which Office would be updated, MSFT doesn’t use their Store to do so. Then again, maybe there’s enough Windows 7 and 8.x Office Insiders that that would be impractical.