My candidate is Michael Conner Humphreys, who played the young Forrest Gump. Obviously his role was key to one of the most influential movies of the 20th century but he does not have a wiki entry. He is mentioned on the Forrest Gump page but for this thread’s purpose, that wouldn’t count. FWIW, Hanna Hall, who played young Jenny does have a page.
I’m always amazed by how many popular and prolific Rock bands don’t have a Wikipedia page.
The Woggles (not the Wiggles or the Wombles or the Buggles, Google auto-correct) are a band from Athens, GA active since the 1980s with, at least, three albums and a butt-load of singles and EPs, and still touring worldwide. I think lead singer, the Mighty Manfred, might be the only daily Sirius/XM DJ without a wiki page.
People who have only a single notable thing about them are usually not worth making a page for. There are, of course, thousands of exceptions to that which could be pointed to, but that’s generally why someone doesn’t get a page.
My brother has a page, and he only has one particular reason to be there, briefly being in a significant publicly visible job, so it makes his entry rather thin, and it could easily be flagged for deletion should anyone want to.
Buggy whips - ya know, the metaphor for obsolete technology being replaced by something new and better. It does appear on the general page about whips, but not on it’s own - does that count?
I actually just ran into this yesterday when I posted about Land Park in the “Shelbyvilles” thread. William Land does not get his own Wikipedia page. He does get a section of the page about the Western Hotel, which takes up almost half the page. He might not be that famous, but he was a wealthy businessman, mayor, and left the money to the city to build the park that’s named after him. And I would argue that he’s more famous locally than his former hotel that doesn’t even exist anymore (If only because he has a park named after him).
Until about five years ago, some time after WWE wrestler Jey Uso earned a shot at his cousin Roman Reigns’s Universal Championship, he did not have his own Wikipedia page separate from his brother Jimmy - they were both simply together as The Usos.
Hmm, should there be a wikipedia page for the most famous person (place, or thing) that doesn’t have a wikipedia page? 
I’m a huge Zappa fan, and one song I really love is Camarillo Brillo. And the main reason I love it is the drums. They’re just fantastic. The drummer’s name is Ralph Humphrey. In addition to Zappa, a quick web search shows he also recorded with and/or toured with dozens of other famous musicians including Al Jarreau, Manhattan Transfer, Natalie Cole, Seals and Crofts, Barbra Streisand, Jose Feliciano, Bette Midler, Captain and Tenille, Richard Carpenter, and Rita Coolidge.
Yet no Wiki page. 
Another musician I can think of is John Trubee.
Here’s an unsolved missing persons case that doesn’t have a Wiki page: The Lost Boys of Pickering.
In March of 1995, six teenage boys disappeared after taking a boat out onto Lake Ontario. They presumably drowned, yet none of their bodies - nor the boat - were ever found.
It’s still under investigation by the police, and many family and community members are trying to get more answers. I suppose some would say it’s not noteworthy enough for a Wiki page, but I would disagree.
The SDMB.