Conversation at the deal table is usually something like "we need X valuation to meet our term sheet with investors so the founders and a few others get paid." The rescue buyer generally doesn't care about what the employees get, in fact it's very much in the buyers interest that the employees don't get too much.
In other words the size of the valuation being bounced around is likely not driven by the value of assets for shareholders but rather the size of the contractual hole in the ground that founders dug with their investors... to escape that hole $X is needed.
Harsh terms yes, but not uncommon.
Preferred shares are common for investors that pay out at a multiple of the common shares, so in an exit the preferred pool can be paid at a dramatically higher rate than common shares.
Funding often also comes with guarantees on return - i.e., if the exit price is below a threshold, the investor gets a guaranteed minimum return before other are paid. This works out for the company if it's a smashing success (the upside is also capped) but can wipe out common shareholders if the company sells for anything less than stratospheric valuations.
This should be a lesson to anyone thinking about working for a startup: a company raised $570M and sold for $3B, and in all likelihood the employees will receive very little from this sale.
In the modern startup fundraising scene, and the way startup equity is structured for employees, if your company exits for anything less than a mind-boggling headline-making valuation, you are almost certainly receiving little to nothing.