Tim Cook was part of a round table of tech leaders (that includes Sheryl Sandberg of Facebook, Jeff Bezos of Amazon, Larry Page of Google, Satya Nadella of Microsoft and others) that met with Trump.
In an article by TechCrunch, he explains the reason for this meeting:
There’s a large number of those issues, and the way that you advance them is to engage. Personally, I’ve never found being on the sideline a successful place to be. The way that you influence these issues is to be in the arena. So whether it’s in this country, or the European Union, or in China or South America, we engage. And we engage when we agree and we engage when we disagree. I think it’s very important to do that because you don’t change things by just yelling. You change things by showing everyone why your way is the best. In many ways, it’s a debate of ideas.
We very much stand up for what we believe in. We think that’s a key part of what Apple is about. And we’ll continue to do so.
The key takeaway is that to change things, we have to show others why our way is the best.
(via Daring Fireball)