They're living in the present and the future seems like a scary concept to them because they know that one of these relationships will have to end eventually, and they're not sure whose heart they'll be breaking. So even trying to get them to commit to a date night next Saturday will leave them saying that they're not sure what their plans are, but they won't actually say what they might be doing instead. As far as booking holidays or asking them where they see the two of you in three years time... good luck.
