ARM had some blunders with licensing changes for one, and then the split with ARM China was bad. Price plays a part. The next thing is that several open designs

ARM had some blunders with licensing changes for one, and then the split with ARM China was bad. Price plays a part. The next thing is that several open designs, including the reference design from Berkley, did very well at optimizing the most common instructions on which easily 90% of computation actually happens. As a result, very early RISC-V silicon showed seriously good performance at extremely low cost. As things are now, RISC-V is becoming increasingly competitive with ARM and x86 with amazing rapidity. There will be a few more hurdles in making RISC-V as performant as x86 or ARM, but given the ISA's open source nature, many eyes will make all bugs shallow.