Click on "Open Petitions" above, and you'll see that the 2 options (All Petitions and Popular) display only petition titles and signature totals.
The absence of expiration dates makes it impossible to quickly determine how much time petitions have left to acquire 25,000 signatures. And because the commitment to answer all those that reach that threshold is the major attraction of this site, expiration dates are one of the first things we need to know.
For example, many of us would probably read and research an appealing petition with only 500 signatures if it still had 29 more days before it expired. Very few of us would probably take the time, however, if it were due to expire the next day!