The Libra project hit a number of obstacles and objections to their original whitepaper. Many of the large fintech partners such as PayPal and Visa dropped out due to concerns over negative publicity.
The Blockchain and whitepaper was changed and fundamental changes made to overcome initial objections and as such Libra was rebranded to Diem in an attempt to move away from any negative publicity over the initial projects plans and whitepaper.
More detailed information here for your perusal: https://www.securities.io/investing-in-diem-facebooks-libra-project-everything-you-need-to-know/69