To be blunt, I don't think "we have a major question closing problem."
I think the system is operating exactly the way it's supposed to.
Questions are put on hold or closed to encourage clarification/improvement.
The expectation is that the author (or an interested third-party) will improve the question to make it more answerable, or to show how it is substantially different from a purported duplicate.
In this case the question, as originally asked, was:
What are winglet and endplate? And how is their functioning?
Where can we found (preferably online) definition of 1) winglet 2) endplate, and Figures of them and good explanation of their functioning ?
This is a variation on the question of "What are wingtip devices and how do they work?" -- while it may not be an exact duplicate it's close enough that it could reasonably be considered one because the answers on the target would lead an inquisitive person to the answer they seek.
Our general assumption is that the members of the community will be inquisitive enough to do a little reading on their own, and if they don't think something is truly a duplicate they'll take the time to update their question to show why it's different and should be reopened.
In this case the OP posted comments clarifying their intent, and the question was then edited to its current form (which references the previous question regarding winglets, but is focused specifically on endplates and how they differ - a materially different question).
The question was then reopened, and answered.
That's how it's supposed to work.
That's how it did work. Ergo, No Problem.