I think there's a practical distinction between the kind of term "omega-3" is vs the kind of term "marijuana" is.

You mostly only find THC/CBD/etc in marijuana; and we mostly only consume marijuana to get those particular active ingredients into our bodies. So you can forget about "marijuana" as a category for describing those compounds, and just speak of the compounds themselves — measure marijuana strains by the presence of those active ingredients; extract and purify one particular active ingredient and sell it; etc. Doing this doesn't lose you anything; in fact, it's a pure win, as the use of precise language gives people a tool to leverage to more precisely ask for the effect they're looking for, and gives suppliers a tool to more precisely describe what they're selling.

While the omega-3 constituent compounds can be treated this way, they are not solely a thing we extract or synthesize to put in precise-molarity-per-dose pills; they're also a thing found in food. Many different foods; with most of them being foods people eat for reasons beyond just getting omega-3s in their bodies. In other words, the "omega-3" constituent compounds are nutrients.

And many of these omega-3-containing foods — fish, for example — aren't carefully cultivated species that have known ratios of the omega-3 constituent compounds that could be put on the label of the food-product. Rather, the ratio of those constituent compounds is pretty much random per individual food item. One salmon at the grocery store has omega-3 fats which happen to be high in DHA, while the next salmon beside it in the same cooler display is higher in EPA. All you can in general about a food product — all a supplier can say, and all a food shopper can generally expect to look for — is a food that is "high in omega-3s."

As long as people are interested in optimizing their health in a loose manner by eating "healthful foods" — rather than taking specifically-formulated supplements — I don't expect they'll let go of the generic categorical term "omega-3." When it comes to food, "it contains omega-3s" is almost always the tightest bound you can put on the "nutritional value" of a given food.