Installing attic vents does not require professional installation. However, the project does require knowledge of attic ventilation, because installation done incorrectly can cause ice dams, resulting in roof damage.
A few other factors also lead homeowners to hire a professional to install attic ventilation, rather than going the do-it-yourself route. One reason is that climate varies so much, making it difficult for homeowners to research the correct ventilation for their specific location. Also, most manufacturers of asphalt shingles require attic ventilation to comply with the terms of the manufacturer's warranty, so improper ventilation can lead to voiding of the warranty.