Many manufacturer's sales reps have taken on some of that responsibility, particularly the hardware specs. However, sales reps that work for the manufacturer also have the main job of selling their employer's products. If specs are written for their own products then they are excluding others in the bid process thus eliminating competition and negotiations. If a distributor is handling the spec writing, they usually have a greater knowledge of a greater number of products and product lines. Although they may like a particular product, they are not totally loyal to it as they do not have sales goals for a particular product line.
Distributors can provide the best product for the job at very competitive prices.
However, the distributors also face the same time constraints as the architect. Another option exists through technology. Computer programs designed to take much of the burden off the writer. These programs still require human input and expertise but can take time off the process. The program is not proprietary so competition still exists while giving the spec writer the freedom to incorporate owner requirements.