There are many different factors as to why digital marketing is important. one reason its important is because it can reach thousands of potential customers as the average internet user has around 8 social media accounts. Another reason is that because of algorithms advertisements in digital mediums are targeted meaning that its more likely to reach people who would be interested in your product. And another point is that the analytic side of this is more advanced as where with tv ads you are unable to actually know if people saw it and bought it because of the ad where as with digital media you are able to analyse the amount of times its been on peoples feeds and able to see how many people have clicked on the add its self. 

Information gathered from: https://www.lyfemarketing.com/blog/importance-of-digital-marketing/