The "culture war" just resulted in the reversal of Roe v Wade denying millions of women with healthcare access. The current and previous presidents both called for depriving people of their constitutional 2nd amendment rights. Even if you specifically dislike the NRA their stated purpose is objectively needed.
To reorient the discussion back on topic, the Sharky Principle is often weaponized by those who don't understand the ongoing endangerment of our basic rights. Even with immediate relevant examples like Dobbs v Jackson. Though it may be broadly applicable across organizations it's important to pick good examples.
Given you mention NAACP I'm assuming your comment refers to US-based organizations.
In that respect "feminists" won a landmark victory in 1973 that was just recently overturned in Roe v Wade. That's one example of the importance of "sticking around".
As all your examples are of groups leaning one particular way politically I'll proffer another example from other side.
Consider the NRA, presumably they don't need to exist as the 2nd amendment enshrines the right in our constitution.
As you may point out that right is under constant threat. Apply that same logic to the groups you're disparaging and you may better understand their purpose.
If plants are sentient that doesn't change much for veganism.