I can take a stab at it..
In no particular order;
1. Usability sucks
2. Massive capex required to replace incompatible kit
3. No real business case, when everything is sitting behind a thumping big NAT / NetScaler.
4. The additional cost of making sure every wheezing business app is IPV6 compliant
5. The cost of MAKING all those wheezing old business apps IPV6 compliant.
6. General business inertia to resist change, and avoid risk.