If Musk had some ideological issue with OpenAI's new corporate structure then why didn't he sue right away?
OpenAI was still effectively sharing their research until last year.
See general allegation "C. The 2023 Breach Of The Founding Agreement".
Microsoft's investment is not the issue. The corporate change is not the issue. They were the first steps needed to create the issue Musk is targeting. Before the Altman drama, Musk probably wasn't paying attention much. Hell, most of HN didn't care either, and we live this shit every day.