Some people see there being an immediate danger to survival and wellbeing right now.
They see it as important to change people's actions right now. The wish to maintain a viable environment for humankind, complete with the range of animals and plants that we have learned to value for whatever reason, is a human desire as well. I believe in rationality and with sufficient and correct information humans will choose to protect their own lives, whatever effort it may take. Sustainability is by definition long term. It refers to the capacity of a given system to be carried on for a very long time.