You don't get high volume processor core into silicon by just hacking Verilog/VHDL in your computer and then send it to the foundry for tape-out and manufacturing like you do with some custom ASIC chip.
Intel and AMD start new microarchitecture design work every 2-3 years. The work must progress in tight time schedule or it becomes outdated. It's highly coordinated effort that requires significant capital investment.
You have to lock in goals, select implementation technology, methodology, have expensive tools etc. Behavioral design, physical design and silicon ramp interact constantly. Problems are solved and there are many optimization and validation phases. You need expensive hardware and access to engineers in the foundry and process you are targeting.
I'm sure there will be many completely open RISC-V cores, but not for the high volume uses or latest processes.