As I followed the simple steps...
In Chrome, go to Settings, then select “Manage search engines.” Next to “Other search engines,” ...Whoa!
Look at all the stuff that was already there!
Why would Google let bhphotovideo.com create an entry in my search engines?
Worse yet, the ones that are in the "Other search engines" are active.
The presentation infers that you have to use the Keyword to invoke them but there's a shortcut that lets them sneak in.
For example, the first entry in my "Other search engines" was "bhphotovideo.com" with a keyword of "bhphotovideo.com". But if I enter "bhp" in the address bar and press "Tab" guess where I go? To a Google search of bhphotovideo.com. There are hundreds of these entries in my Chrome "Other search engines". And there's no way to delete them en masse.
There seem to be at least 2 ways these get added. 1) Google will discern that there's a search box on a page and add an entry or 2) the site will use an API to add an entry.
There are discussions of this here and here. Oh, yes, the Chromium developers know about this and have marked it WontFix. See Comment 7.
There's even a Chrome extension that addresses this that I haven't tried.