Not to be pedantic, but it does have a certificate; it's just not one that's widely trusted. Details from Firefox on my MacBook Pro:
The shoebank certificate was issued by Symantec.
The problem is that Symantec certificates issued before 2016-06-01 are not trusted anymore. Any certificates signed by such a Symantec CA is also not trusted anymore:
Distrust of Symantec TLS Certificates – Mozilla Security Blog
A Certification Authority (CA) is an organization that browser vendors (like Mozilla) trust to issue certificates to websites. Last year, Mozilla published and discussed a set of issues with one ...
blog.mozilla.org