My guess is that they realized it fits into the "corporations are evil" narrative that has become popular with many angry people on twitter recently, and then decided they didn't want to feed into it.
I think the author has made a false assumption about how lists are typically used in Haskell. Being algebraic datatypes, lists in Haskell are built on a foundation of universal algebra. The operations that you perform on them are inherently inductive: process the head and recurse on the tail. The most common tasks in functional programming, such as program analysis, fit into this paradigm nicely. So including "(Mostly Not)" in the title is misguided; the designers of Haskell and other functional languages knew what they were doing when they decided to make lists prominent in accessible in their languages.
I think it's more about hiding college credentials than hiding the portfolio.
It would be great to allow programmers to show their portfolios, but that would likely enable interviewers to google them, giving away their backgrounds.
I have a few interesting projects in my portfolio that I am proud of, a reasonably high CS GRE score (a test which is unfortunately not administered any more), and a moderately good topcoder history. However, after being told by an HR person that they would not hire me because of the college I went to (a for-profit college) I started to view the relation between hiring and credentials as illegitimate. So for that reason I hope TripleByte catches on.