There were only couple of options for this merger to take place.
1. Dow and DuPont merge without any further plans to split. This wouldn't fly with regulators as combined entity will have too much power in US as well as worldwide. Not only US regulators but also regulators in EU and Asia will be very interested in vetting such deal.
2. Dow and DuPont swap the agriculture and specialty products divisions and merge the materials division with recent DuPont spin-off Chemours. This wouldn't fly with regulators either as both Dow and DuPont will have too much power in their respective segments.
If Dow and DuPont would have gone with option 1, the regulators would have come up with their own plan to divest certain businesses to approve merger. Instead, Dow and DuPont are offering a future split solution by proposing to split in three portions that will get them closer to option 2 with some regulator-driven divestment.
I will not be surprised when and if merger and split goes through, we land up with the second scenario anyway. Agriculture goes to Dow with HQ in Midland MI, Specialty products goes to DuPont with HQ in Wilmington DE, and Materials goes to Chemours.