I *think* that has to do with the Microsoft Edge extension. You need Enpass Bridged (5.6.2) to get Edge support. If they didn't release that version, then Edge users wouldn't have any solution for Enpass.
I get your point: why not wait with the release of 5.6.2 untill it supports ALL browser extensions? Sadly, that would mean some users wouldn't have any option at all...
At least now everyone should be able to use Enpass for their favourite browser, if they install the correct Windows application (5.6.2 (Bridged) for Edge, 5.6.0 (Traditional) for Firefox v57, other browsers are supported on both).
Yes it sucks and is confusing as hell. But we can continue using it for now and we are talking about their free desktop versions... I can wait this out and am looking forward to the next release of Enpass Bridged in the Microsoft store.