Ann: DOW: Presentation - Offer for Spotless & equity raising, page-35

Its a couple of months before the deal closes.
There's a very real risk that SPO disappoints (like it has with every other earnings) and DOW walks away, thereby creating a huge overhang which means stock will go below the pre-bid price of ~70c
DOW's 19.9% stake is also good protection against a counterbid.

If you're a very high conviction short, nothing has changed except price. Which means you're just gonna short more!