Budget and schedule constraints are important, and binding, factors

Regulatory demands create strains and stresses internally

Selection of solutions is affected by competing internal forces 

There may be significant risk in a decision to switch vendors

It's often unclear whether one should buy a vendor's solution or build similar capability internally

Vendors' capabilities may be less polished, and their staffing levels lower, than initially broadcast

There may be uncertainty regarding vendor commitment to service and on-going maintenance

There are many choices offered in the marketplace, but often no clearly superior offerings

Techniques utilized by many vendors are so similar as to appear indistinguishable

Increasing complexity of solutions has made them difficult to evaluate

Vendors may be good at 'spin' and representing 'vapor-ware' (tools that don’t yet exist)

There is a lack of transparency. Some tools are offered as 'black boxes'

Vendor capabilities and inclinations may be affected by different philosophies and historical evolutionary paths