Because Twitter's failures are all semi-public anyways. He's scapegoating. Attacking them for these things firmly attaches blame to the previous management and

Because Twitter's failures are all semi-public anyways. He's scapegoating. Attacking them for these things firmly attaches blame to the previous management and becomes his first success as a manager. It's what always happens, but he did it proactively. It won't hurt Twitter's value because it never really had credibility, but also doesn't need it. Nobody is going to get up tomorrow and say "I was going to tweet this, but I'll rumble it instead because Twitter has lied to the FTC since 2011!"