Simply put: technology advanced to superscalar, OoO cores & 64 bit multi-core cpus. These advancements took decades to pan out. Both x86 and ARM had to 'ride t

Simply put: technology advanced to superscalar, OoO cores & 64 bit multi-core cpus. These advancements took decades to pan out. Both x86 and ARM had to 'ride the wave' when that tech came along. RISC-V otoh can pick up the result of those advancements, piece it together for a new ISA, and go. No waiting-until-tech-advances other than the wait for design work & prepping those designs for mass-production. Both of which can take considerable time. But not decades.