Because you fire everyone who knows how the systems work. And while Evernote sounds like a weekend project to everyone on HN, I'm certain that over the decade-plus of its existence that it has accreted a lot of technical debt and 'FIXME: we should rewrite this spaghetti' all over the codebase. You've now replaced anyone who knows how the product actually works with people who don't understand the product and aren't going to be incentivized to /care/ about the product at all. The codebase probably needs a rewrite, but the people who understood all the issues of the codebase are gone, so any future rewrite is just about guaranteed to fail.
So what you're left with is a skeleton staff who just keeps it running, it won't grow it won't get new features, it'll stagnate and the profits will come from cutting staff even more aggressively. It is definitely a zombie product now.
And any remaining users should already have jumped ship. The staff remaining won't know how it all works, they'll have cut staff down to the bone, and there's a high likelihood of everything getting hacked or just constant service interruptions.