Because there are a lot of uninformed investors out there that have absolutely no idea how bankruptcy works. Especially Chapter 7 bankruptcy, which guarantees, BY LAW, that the equity is cancelled.
For more proof that individual investors don't understand bankruptcy, look at Hertz. They stated over the weekend that the existing common would be cancelled without any payments to shareholders, but the stock still has a $200 million market cap. Insanity.
The stock will trade until it is cancelled. That can happen at any time, without warning.
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