Well, you're free to be wtf'd by whatever strikes your fancy. I just don't find it all that odd myself.
I'm pretty sure it's mostly because I work at a library? It's genuinely, like... pretty unusual to see kid targeted material like this to begin with, and especially at so long a delay.
Kid's books being produced in relation to an adult/general audience sitcom series from the 90s/early 00s happens, apparently, but it doesn't exactly happen
often -- and by not often, I mean I've been working in a library's cataloging department for nearly a decade now and if this isn't the first time I've seen anything like it, it's my proverbial second nickle.
Movie/TV tie-ins in general do happen fairly regularly for the book market in question, but it's really rare it's for something like Friends.
... actually kinda' curious if there
is anything else like it, now. Quick lookabout shows there are some others out there (mostly seeming to come out of the same publisher; the author of the friends things did one for seinfield and gilmore girls, and they all seem to have been published by Little, Brown Books for Young Readers, but there's a very small smattering of others), but it's definitely a micro-niche, ha.
Though they've apparently put out a small set of golden books of similar intent pretty recently, too. Someone's definitely trying to tap into a nostalgia vein in an odd way, heh. Going to be interesting to see if it catches particularly well, I guess. Maybe we
will get a rocky horror picture book aimed at six year olds sometime in the next couple years...