I have no idea and no data at all, but I can speculate at length:

When acquired, the firms had a lot of liabilities of wildly unpredictable magnitude, so they weren't allowed to declare bankruptcy.
The claims against the acquired firms have finally wound down to the extent that Berkshire is now allowed to put them into bankruptcy, drawing a line under further liabilities.
Perhaps in conjunction with a capped guarantee from Berkshire itself for the small remaining tail.

Since the firms had ceased operations prior to Berkshire having acquired them, it would be interesting to know what the assets were.
They weren't operating assets, so I'm guessing it was a pile of cash or securities (and maybe insurance policy interests) that had been earmarked for the liabilities.
Maybe Berkshire was pretty sure the liabilities would ultimately be less than the assets acquired so thought it a good deal to buy the companies, presumably for a song, to get the excess assets and secondarily the time benefit of the float acquired.

See? You don't have to be a chatbot to make stuff up.

Jim