goodwill

Dear Sir,
If the reason for not recognizing an internally generated goodwill is that it is an item that is difficult to identify and measure reliably.
If a merger or an acquisition that measure and identify goodwill reliably and fails at the end (we don’t want at the end). in this case why we don’t recognize goodwill however it measured and identified reliably by a fail merger or acquisition.
if not what is the other reason?