According to its Hot Chips 2020 presentation, AMD originally planned on having Renoir top out at 6 cores. However, TSMC's efficient 7nm process allowed AMD engineers to design an 8-core CPU within limited silicon and thermal constraints.
https://www.notebookcheck.net/AMD-s-Renoir-architecture-was-originally-planned-to-top-out-at-6-cores-but-TSMC-s-7nm-process-let-engineers-bump-it-up-to-8-cores.488501.0.html