The poison pill was mostly developed at a time when the alternative was him selling all the company assets and leveraging the company to load it with as much debt as possible then give out as large a dividend as he could before selling off the stock leaving the company insolvent and everyone out of work.

So imagine a company taking $100 million in debt, giving all that out as a dividend then the stock price tanking through quick sales. Poison pill keeps the company going and avoids that fate.