What you say is contradicting.
He did not find the material.
He did find material that would burn the longest.
Did Thomas Edison find new material that would last the longest? NO
Did Thomas Edison alter the existing materials to make them last longer and be marketable? YES
It was Joseph Swan who found carbon as a cheap alternative to light bulb filament. However this filament would still burn out after awhile.
What Thomas Edison did was to make the carbon filament thinner and looped it as well as vacuum seal the bulb more efficiently.
Thomas Edison invented the "Edison Light bulb" which is less of a brand new creation and more of an improvement on a concept that's been around since 1802. You can credit Thomas Edison for making marketable light bulbs which is indeed a scientific break through, but that still leans him towards being a businessman than a full-on inventor.
May be I'm not good at wording them but I'm sure you get the point that I've been trying to do devil's advocate all this time since I myself didn't like Edison that much (even when he's played by one of my favorite actors in
the movie).
My point is this is how general mass perceived at that time :
Let's say a father and kid were taking a look at light bulb.
Then the kid ask, "Dad, who invented the lamp?'
Most likely the father will simplify the answer by saying, "It's Edison, son" since the light bulb was produced by Edison Electric Illuminating Company.
This went on many decades so that Edison's name become a synonym for light bulb.
It's oversimplifying and it isn't true but it's understandable.
If my kids ask who created Toe Jam, Ecco the Dolphin, and Shenmue.
most likely I will simplify the answer by saying, "It's SEGA, son"
while the answers are supposed to be Greg Johnson & Mark Voorsanger, Ed Annunziata, and Yu Suzuki.
Or simplify the answers with Disney for Mickey, Donald, and Uncle Scrooge creator.
They are indeed a common mistakes but I can understand why it's like that and why it was hard to be fixed.