Why? For $ of course. Plenty of people screw their own country for cash. Joe Biden and Bill Clinton come to mind.
It is likely that some group like Al Qaida is coordinating the riots and obtaining the weapons, possibly through organized crime. Ukraine is a pesthole of corruption and has been since the fall of the Soviet Union. However, American and British intelligence, if they wished, told Zelensky or the Ukrainian mafia to desist, if the goal were to protect Macron. The French leader has been stepping out of line in his desire to have France negotiate with the BRICS financial group. Defection or even flirting is unacceptable. So supporting the riots may be the American and British method of keeping Macron in line.