Firstly, GM has many manufacturing facilities and ecosystem suppliers in North America; Nortel out-sourced manufacturing years ago.This has attracted political action on behalf of GM.
Secondly, both have been spread too thin, in terms of brands for GM and products for Nortel. This has contributed to lower competitiveness.
Thirdly, Nortel has been, in general, better aligned with customer needs. This customer focus is a plus for Nortel, while changing the Detroit culture is a major challenge for GM.
Finally, in both cases, company executives have their hands full and are not in full control of their destiny.