Right now GE can hide behind opaque accounting and promises of future cash flows. Selling the parts means converting assets to cash. That would remove any doubt as to asset value and eliminate any hope of future cash flows.
The worst case scenario is that the cash would not be enough to cover the liabilities and the company would go bankrupt leaving creditors out of pocket, shareholders holding nothing and employees out of work, losing both pension and outstanding compensation payments.
GE has a lot of intangible assets that can't be converted to cash, tangible assets that are worth less than book, and is in a weak bargaining position since potential buyers know how bad they need to sell.
Excellent post on why GE is not better off breaking up in parts. Posted by @Sl8gjNs-1cjm.