@Jennifer A. I can't speak for your area but here locally there are a few factors that figure into it. Some people do take the option to sell, however most of the properties we've seen and dealt with make it to the auction sale due to a couple specific actions, or inactions.
First, most homeowners believe they can stop the foreclosure and fix the problem. This could be because they think it won't be that hard to get caught up, believe the bank will work with them to refinance etc, or are currently doing some sort of program that is a loan modification. Remember, I only know the actions and policies of our local financial institutes. However, even if they are in a loan modification process, until it's approved, the bank expects the payments to be current and will not typically stop the foreclosure process until the loan has been completely reinstated. The most common form of a loan modification by the largest bank locally results in the past due amount being rolled onto the back end of the loan, and payments will be expected to be paid as if normal from that point on. This typically doesn't solve the problem and only delays it. An actual loan modification, meaning decrease of interest or balance or restructuring of the terms happens very infrequently. I've recently talked with 3 different homeowners who have been in negotiations with this bank attempting to find a resolution for a duration of no less than 6 months and one has been dealing with them for a year and a half. They constantly say they need more info for the underwriters or to much time has passed and require updated paperwork of w-2's and other financials. They stall and give the homeowner the "we are working on it" excuse. Most get so frustrated they just throw up their hands.
Secondly, once they get so far into the foreclosure process, most realtors don't feel comfortable attempting to help sell their home because they can't guarantee the closing before the auction date due to the restrictive lending and that the bank won't typically stop the foreclosure even if there is an offer on the table unless the past due amount is completely caught up and the loan reinstated. In our area, a home loan that is 4-5 months past due and in foreclosure will cost about $10k to reinstate. As you can see, once they reach a certain stage of the foreclosure process, it's almost impossible for them to stop it. Normally. That's where investors come in. We can do things that most banks and Realtors aren't able,or won't, do.
Lastly, some people just become ashamed, depressed, stressed out and do the "Ostrich Syndrome" which is to say they ignore phone calls, knocks on the door, and mail contact, bury their head in the "sand" and hope it all goes away until it's too late to do anything.
Hope this gives some insight. If you ever get a chance to talk to someone going through a foreclosure don't be afraid to just talk to them, ask why they haven't sold. After a while, you'll start to see a pattern.