Several things contributed to Nicole's non-success in the US, the sum's being greater than the parts:
"Pussycat Dolls." Yeah, no. Not going to fly in Mainstream America. Plus, according to Wikipedia, the group started out as burlesque. Miscue #1.
"Scherzinger." I mean, Cary Grant changed his name from the simple "Leach." Her Miscue #2.
Desperate chasing of the younger and gayer Lewis Hamilton, who, after many years, wouldn't put a ring on it. Plus, though he was and is a phenomenal F1 driver, Lewis is neither American nor in a traditional American sport. Should have gone after an Andretti or an Indy driver. This "relationship" was Miscue #3.
And a factor NS could not change: her ethnicity. Being Hawaiian, she seems neither here nor there, a week bit too exotic. Sure, Tiger Woods might say he's "Cablinasian," but he's Tiger Woods. And he looks Black.
She was superb on "Dancing With the Stars," but even though she won, the pretense that she was an amateur turned off some of the audience.
Now she's 40. So it's being a judge on talent shows time.
Ultimately, Nicole Scherzinger has been successful in her chosen carer, with a top-selling group and with many award nominations. But her success is of the Robbie Williams, Kylie Minogue, and Westlife type, aka,
"Not here."