Installing batts generally requires nothing more than a cutting tool, staple hammer and minimal personal protective equipment - no machine or power source needed. With spray polyurethane foam, a complex combination of equipment is required. This equipment adds complexity and time to every spray foam job.
Imbalance in pressure or fluctuation of temperature can result in poor mixing and a product that may deliver inferior thermal performance, or worse, a product that does not cure properly and requires removal. Not to mention, all spray foam equipment must be cleaned and recalibrated after each use for quality installation of product.