I was under the impression it was partially due to him feeling the ‘U’ made the words feel “too French”, and he supposedly really hated the French (apparently he was a bit of a fan of the ol’ racism), but mainly he wanted something new and uniquely American - and English spelling was even more regional, wild and inconsistent back then, so he hoped to simplify it, bring it some consistency, ideally whilst also telling the French to piss off.
“Our Nige, he’s just like a normal bloke he is, you know. He’s one of us. Rather than being a private-school-educated, upper class, millionaire career politician with a background in the financial sector, he’s just a normal everyday ex-financial-sector career politician, that’s also a millionaire, and also upper class and also private-school-educated. He’s only been a politician for 25 years, so he’s pretty new at it and a fresh new anti-establishment underdog. He’s just a normal bloke trying his best”