The US has 2 parties, and people tend to be die-hard supporters of their "team", as if politics were a sport. To be disavowed by the supporters of your own party, in the US, you'd need to at least commit a genocide of some kind.

France has many, many parties. Parties are born and die regularly. Macron's own party, La France En Marche, didn't exist two years ago and now it is the ruling party. On the other hand, the Parti Socialiste, one the historically biggest parties, which ruled France several times over the past century, all but entirely died overnight after Hollande's presidency. So instead of having 2 camps, and everyone having to support one or the other, France has dozens of camps and it is very easy to change your allegiance from one to another, or start your own.

For reference, Macron won the presidential election with 24% of votes in the first round, so he actually gained 2% approval.