As quoted from the linked post.
It looks like you’re part of one of our experiments. The logged-in mobile web experience is currently unavailable for a portion of users. To access the site you can log on via desktop, the mobile apps, or wait for the experiment to conclude.
This is separate from the API issue. This will actually BLOCK you from even viewing reddit on your phone without using the official app.
Archive.org link in case the post is removed.
You’re not wrong, but also I’d like to move away from the world of “site:reddit.com” being the go-to troubleshooting/advice-seeking search, and my posts turning up in such searches would be driving traffic to reddit, which I don’t want to do. I also don’t want my account history used for advertising purposes, and across the life of an account I tend to share more personal specifics than I’m comfortable with sharing in aggregate.
But you’re not wrong, either. I can see both sides of this one.