There will likely be new equity and ticker but unless it was stipulated in the Reorganization PLAN that former shareholders would receive any part of the new equity then former shareholders are wiped out completely.
Your second question: Yes, it is typical for shares to be cancelled because the former equity is considered burdensome to the Secured Creditors agreeing to the PLAN. Once in a rare while former shareholders may receive a token amount of the new equity, or warrants to buy the new equity at a reduced price, but to repeat, those instances are rare.
Your third question: "why do people buy shares of a company filing Chapter 11?".....poor research on reorganization BK's; or high risk gamblers hoping they can flip shares for a profit before the shares are cancelled; or extremely deceptive message board posts FALSELY declaring that 'this stock will be different'; or any other nonsense reason.
To bite the worm of incite is to bite the HOOK of the antagonist . They win .