What's an artist who depends on the platform to do?

Labels can only write up contracts giving them rights because they pay for studio time (given them a financial buy-in to the creation of the music) and pay advances against royalties. Not so for indie distributors. I don't know if there are specific applicable laws, but it's absurd enough that everyone would immediately drop Bandcamp.

Music royalty rates, for physical records, radio and internet streaming, are also determined by a panel of judges: the United States Copyright Royalty Board.

I guess that only works for Darth Vader.

A small team can quickly copy how it works and get all the artists to move platform if they were to shoot themself in the head. Right now this doesn't happen because Bandcamp functions and exists and has a reputation for musicians.

Lose that, all the artists start looking for a new home and someone will make an alternative quickly.

This may have been a last-minute accelerated deal process where Epic would have all but shuttered Bandcamp if a buyer couldn't be found, before they needed to announce massive layoffs to assuage investors. Songtradr is given an opportunity to see the deal, wants to ensure Bandcamp's survival in its current form (because its demise would hurt the entire ecosystem Songtradr depends on).

But Songtradr isn't given time to put together a transition plan or identify the exact legal path to deal with the union (especially given that they're in an entirely different country with different labor laws!) and not expose themselves to liability. So they announce conditional openness to the acquisition (per the link above, the transaction hasn't closed yet), and this at minimum gives Bandcamp a stay of execution while they identify next steps.

Now, they've identified at least one next step - how much of the current Bandcamp costs they can carry during the transition - and that's 50% of current staff. A tough call to make, but if the alternative was shuttering the service, a very justifiable one.

They maybe can’t prevent it, but they could leverage BC/Epic/whomever into providing some kind of decent severance for those left out in the cold. In theory.

Their entire minimum revenue guarantee scheme to lure over indies and publishers is apparently extremely expensive for Epic and the store has yet to turn a profit on the whole. Before, they could run it off of Fortnite profits alone. That said, Sweeney has admitted that well is basically running dry and it's why they've been doing layoffs and the like everywhere.

If a company is in trouble, the first thing on the line are the subsidiaries and Bandcamp is a questionable acquisition on the Epic rep sheet, being a music store for a company whose main business is making videogames and selling a gaming engine to people. That means it either goes under or is sold off because it's seen as an irrelevant "aside" subsidiary.

There was no investor pressure.

this is incorrect. in addition to whatever lord you are speaking of, I also know. (unless you meant me, but even then, I think others share this knowledge.)

Epic bought Bandcamp to use it as a weapon in various lawsuits against Google and Apple over their pricing models. Bandcamp joined a suit against Google over its Play Store pricing in particular.

it didn't go anywhere, because Bandcamp already qualified for media app pricing, which rendered its role in the suit meaningless. but that was why Epic bought Bandcamp.