You have a successful business with an offline (non-Internet-based) marketing campaign which is achieving some results.
Why do you need a website?
People will often Google something they encounter in the real world in order to verify it and check its credibility.
By not having a presence online, you effectively hand your brand reputation and all related conversations on that channel over to someone else. Either a competitor or a random third party, both of them very much with their own agenda.
Also, if you are interested in getting new Leads, Prospects, and Customers from the Internet, then you need a website. Your online reach can potentially be quite larger than your offline reach.
You can have a full fledged web presence where you are actively using your web presence to supplement and provide credibility for your offline marketing campaign.
If you would like some more information on how to leverage the latest trends for your business, contact Steve at email@example.com or call.