They didn't lose the website address. They send out hundreds of thousands of email and are hoping their potential victims will respond and tell them the website. Then the scammer can continue on to the next step of the scam, which is to pretend to want to buy individual pieces and then overpay with a counterfeit check and ask to have the difference wired either back to them or on to some fake shipping company.
---------- Forwarded message ---------
From: Kevin Waters [firstname.lastname@example.org]
Date: Wed, May 9, 2018 at 10:13 PM
Subject: Artwork Inquiry
My name is Kevin Waters from Jacksonvile, Florida. The images on your
website are so fascinating and so vivacious, looking at each piece of work
i can easily see that you added so much dedication in making each work come
out to life, unfortunately i lost the website where i first saw your work
but i was able to save your email address. I will like to purchase some of
your work for my wife as a surprise gift for our 20th anniversary. Please
kindly send pics and prices of some of your art which are ready for
immediate sale within price range $500- $5,000, I could be flexible with
price. I am writing you because i need your assistant to get back to your
website so as to be able to retrieve the details of your work that interest
me or send me images of some of your new works with price.