https://app.travis-ci.com/signin
I understand why they are doing it, because they have to pull from GitHub, but it's not the only way. They could create a regular user on GitHub and ask people to let that user pull from their repositories. Obviously it's more trouble for the user, it would harm adoption and growth, that user could be banned and halt all of Travis.
Travis is the only site I have ever used in that way, because I have a customer that uses it. With hindsight I think that I should create a per customer account on GitHub, just in case something bad happens to Travis.