Federer not being American makes him underpaid and largely unknown in the U.S.
For him, he is grossly underpaid compared to what Michael Jordan and Tiger Woods were getting. And a lot of people don't even know who he is in the U.S. Non-tennis fans know who people like Woods, Jordan, Lebron, Tyson, etc all were/are. People even know Agassi.
Actually, his sponsorship portfolio makes Jordan's look small. Jordan was the king of the time but not comparable to the top endorsement deals of today in dollar value.
In addition, Federer - like Woods, Jordan, Beckham - is one of a rare breed of athletes who has
significant recognition outside the fans of the sport he plays. It's not in his favour that tennis can't come close to the popularity of soccer globally or basketball in the US (for example) but it
is in his favour that he is in an individual sport. Team sportspeople rarely ever get notable endorsement deals with high-end brands unrelated to sports - because they have very little opportunity to forge any 'classy' appeal compared to individual sportspeople, no matter how amazing they may be at what they do.
Federer is a dream combination of magical sporting talent which has been realised in his results (unlike
many other legendary talents - David Beckham for example has too often been the "almost" guy and achieved far less than his talent promised), has general good looks, he's well articulated when he speaks, is widely praised by the all-time greats from tennis and other sports
and even by his closest rivals. He has barely put a foot wrong publicly for years - he's even almost always presented like he just stepped out of a stylist. Over a long period of time all these things combined have raised his stock so much it's got him into the frame for companies like LVMH, and they do not make endorsement plans on a whim. They will have followed him and perhaps even been pitching him for some time before this deal came to fruition.
Whether you love or loath him or think he's all about money
or whatever, Federer is and will continue to be for a few years the benchmark for individual sporting endorsement deals globally. The way they've (IMG and with Godsick since leaving them) carefully seen him associated with a cluster of complementary brands is not at all by chance.