100% of companies require a way of communicating with other companies/people, and federated email and phone calls are extremely common ways (granted that non-federated means are becoming more popular, and I can believe there are a few companies whose only communication with the outside world is via non-federated means).
Companies have lists requirements for their tools and "not federated" isn't one of them, it's just that so far non-federated tools already fullfil the other requirements. Once Element is mature enough (and I'm sorry, but looking at the incoming issues on https://github.com/vector-im/element-web/issues?q=sort%3Aupd..., it doesn't look like it yet), then hopefully more companies will start considering it.
Also, some companies (at least some people in the one I work for, so I'm extrapolating) want to be able to text chat with other companies/people, and they currently do this with Teams (which requires both parties to have a Teams account). Slack allows this too if I understand. Federated chat would also give them this, so it is something they need, even if they don't realise that.