The issue wasn't that “Skip” was hidden, it was that two default-styled buttons were shown.
And why one should be different than the other ?
It's 2 different choices.
Making them different risks preferring one to the other.
Because it's their website and they prefer one to the other?
That's a dark pattern and unethical in a lot of situations.
As sibling mentions, the issue is with overusing the default style. Another pattern could be to use a secondary outlined style, making skip as prominent as the default.