Because he cannot stay as president a third term, so he's trying to look like it was his choice.

He's probably got quite a few oligarchs eager to put him on their board.

At least in Finland the ex-politicians usually become lobbyists, public speakers and leaders in private organizations.

I wouldn't be surprised if it was similar in France.

he's far too young to declare retirement

He'll be 50 which isn't too far from Obama leaving office at 55, and he effectively retired afterwards.

He'll spin up a consulting company and send invoices for "consulting work" to all the companies with backs he's been scratching the last decade so they can scratch him back.

He's French, he's got years of sitting at pavement cafes, drinking espresso and smoking Gitanes to catch up on.

That's the point, they have no incentive to abuse it - also it's mostly an advisory position, saying "nope, this law you're trying to pass is unconstitutional, this line can't stay". They don't actually do anything themselves, and I've never heard of a case of someone trying to bribe them to reject something.

Didn't Macron raise the age of retirement for men? /s