They see your site, and send you an email. Then you have their name and email address, so you can follow up in a more personal manner. When your visitor clicks on the link, an email form is opened and the visitor can send you a regular email. Email has some problems. Email is boring.
Nobody likes to type in email messages.
It's not really a part of your web page. The email form opens up into a big blank page. It's hard for your visitor to get started. Email has no structure, so it's difficult to get all the information you want.