Most business loans are non-recourse.  The only security the lender has is its collateral.  Thus, if the collateral is no longer worth the mortgage balance, savvy businesses will simply default.  It would be cheaper to find a new building and move if the bank calls its bluff.  But, the banks know this as well... so they generally "re-negotiate" the terms of the mortgage and write down the principal.

For some reason, this doesn't work for homeowners.  The banks would rather foreclose and take a larger loss, than simple take its lumps and write the principal down to the value of the collateral.  part of this may be due to the bankrutpcy laws that do not allow a debtor to cram-down the first mortgage on a residence.  This prohibition does not apply to businesses that file bankruptcy.

And, the effect of a bankruptcy, or strategic default, on a homeowner is much more serious than it is for a large business like American Airlines.  American Airlines will still be able to obtain financing after this move... a similarly positioned homeowner will be saddled with credit score that may make it impossible to buy a new home, or even rent in some cases.  The difference is usually the nature of non-recourse debt - American Airlines probably has no liability beyond the pledge of collateral for the loan.

We need to change the laws to give the homeowners more leverage to negotiate with the banks for writedown of their principal.  But, once again, homeowners do not have the lobbying power of big business.