Blue jeans have been around since 1873 and there is no reason they should fall out of existence in the future, in favor of "Star Trek Civilian" -- a line of clothing that seldom looked real.
I am pretty sure that toga's were around for longer than 131 years, yet they eventually fell out of fashion.
But - you're mistaken in thinking denim had "[fallen] out exsistence in the future". Kirk and Bones wear them on their camping trip in Star Trek V.
"Star Trek Civilian" usually looked pretty ugly, especially the sweaters and dresses.
Togas are rather interesting... of course they wouldn't make a comeback in our society, since for one thing there would be the cry of "OMG, that man is wearing a DRESS!!!" and for another, they're really fussy garments to drape correctly. They're not very practical - I can't see a bunch of men wearing togas going about their daily business in modern society without tripping over them, getting them caught in elevator doors, and finding it impossible to carry stuff. And what kind of footwear could they use that wouldn't look incredibly stupid? Sandals are impractical in our climate for much of the year.
Mind you, the class of people in ancient Rome who wore togas also had slaves to do all the practical physical stuff for them anyway, including draping them correctly in the first place.
Something definitely changed in the world of civilian fashion between Kirk's era and Picard's era. Check our the getups everyone's wearing in Search for Spock, then compare that to what we see on DS9. We went from hip couture to space spandex overnight.
Considering that it was supposed to be 75-80 years between Kirk and Picard, that was hardly "overnight."
Let's not forget the eye bleach we all needed after being subjected to the sight of Matt Decker's genitalia being smashed up the inside of his TMP catsuit...
You mean Will Decker. Matt Decker was his father.
And yeah, that's one camera shot that never should have made it anywhere but the cutting room floor.