What is the age range they are classifying as young? Are they talking like teenagers or mid-20s to 30s? The thing with Star Trek that I think attributes to the non-fans not watching would be the stylization. Going back to the comparison of MCU, HP, and Star Wars: they all have something unique (be it the directing, photography, acting, writing, music, special effects, etc.) that if you pay attention for a significant period will find. Star Trek is no different. When you watch a MCU movie or TV show you probably see the sleek costumes and fast paced fight choreography. With HP, it was probably all the special effects, makeup and set design. For Star Wars it might be the writing, special effects and music.

I’m being non-specific here of course. Star Trek like I said is no different. There are visual and non-visual language being utilized that we find enjoyment in. For anyone not currently into these properties, it could be difficult to enjoy. Especially if you haven’t been someone who watched these properties from a young age or from the early years. For example, if you had someone exposed to only the Kelvin Timeline try to watch TOS or TNG with no context for how it relates, a disconnect might form. Visually those series are not as sleek or modernized as those movies.

As for the comparison to video games… that is simply a different medium. What appeals to one person to the next will be hard to gage. That doesn’t preclude the likes of Fortnite players from enjoying Trek, but culturally that kind of entertainment is very different from what a kid who grow up with TNG was exposed to.