why?
Because it had similarities with "More Bounce to the Ounce" (1980) by Zapp.
Uptown Funk
 In 2017, Lastrada Entertainment filed a lawsuit citing similarities with "More Bounce to the Ounce" (1980) by Zapp. 
uptown funk you up uptown funk you up song UNANSWERABLE is this funk a song? Yes, by Mark Ronson. from what is it influenced? It is a funk-pop, soul, boogie, disco-pop, Minneapolis sound track, with a light EDM influence. has anyone lodged any case against it? Yes, by Lastrada Entertainment.
wiki:12044597
Uptown Funk [SEP] Controversies and lawsuits
In 2017, Lastrada Entertainment filed a lawsuit citing similarities with "More Bounce to the Ounce" (1980) by Zapp. In 2018, the Collage and Zapp lawsuit were dropped, with no word if there was a financial settlement. The track drew comparisons with the theme song of "The Really Wild Show", a BBC children's nature program. When Ronson was asked if he heard similarities between "Uptown Funk" and the theme he said "Oh, then the horns, I understand what they're saying, yeah, we owe a little bit ... all equally influenced by Quincy Jones".