Maybe their core demographic wasn't people shopping for an agency. All businesses are different but when I worked on the design of an agencies own site we discovered that very little work comes in through the website. We had two choices about whether we tried to increase the amount of work we got through the site or used it for a different purpose. Perhaps they had the same decision to make and came to a different conclusion.
Sometimes agencies want to use their site to increase their recognition in their own field or even to win design awards (seems tacky but it happens).
Maybe their core demographic wasn't people shopping for an agency. All businesses are different but when I worked on the design of an agencies own site we discovered that very little work comes in through the website. We had two choices about whether we tried to increase the amount of work we got through the site or used it for a different purpose. Perhaps they had the same decision to make and came to a different conclusion.
Sometimes agencies want to use their site to increase their recognition in their own field or even to win design awards (seems tacky but it happens).