There was no mention of this in the previous jams. 
I understand that you want to warn first-time authors that this is a daunting and challenging jam, but I find it a little too patronizing. I consider that I have minimal experience playing text adventures games, having played a handful of games, mostly qbasic stuff, many years ago. I've played tons of p&c graphic adventure games, and read many CYOA books. So it's not like narrative intricacies and puzzles are foreign to me. 

I understand what you're saying, it's just that it comes across as gatekeeping. And since I know you're not gatekeping the whole text adventure genre, then what's the point? It's weak, it shouldn't be there.

It's there because we had bad experiences with newbie authors last year where the games they wrote were definitely not suitable for beginners and we were crticised for that. Beginner-friendly games is the whole point of this competition.

We do not discourage newbie authors, but we try to explain what they're getting themselves in for and to get a mentor. In your case, point 'n' click, choose your own adventure (CYOA) and narrative works are not appropriate background experience for this competition, as it's all about parser-based text adventures suitable for beginners to the genre.

Writing a text adventure is hard. Writing a text adventure suitable for beginners is very hard. Writing an in-game tutorial is very, very hard. Even very experienced authors have difficulty with this, which is why very few text adventures have an in-game tutorial. If you think you have the skillset to write such a game, you are more than welcome to enter the competition.