My understanding is that this ability for guests to ask for dates that are closed on the calendar is only for those that offer Instant Bookings which may go to explain why some of the calendars you've looked at Joan don't have that feature.
I'm not on IB and I don't have that extra caption that @Andrea6232 shows in his screen shot with the option of taking it off.
Ahaaa! That makes perfect sense! It wouldn't make sense to use this on listings that are already using Request to Book, but only for those with IB. Perhaps this is to encourage Hosts who use Instant Book to provide more availability further out, kinda like the optional setting for Advance Notice? Let me check some addl listings using IB: