[FullyFunctional]

The specification (http://riscv.org/riscv-spec-v2.0.pdf) clearly states the reasons. It has nothing to do with political/legal issues. There are very good technical reasons for designing a new ISA.

That RISC-V resembles MIPS is a testament to what was good about the MIPS design, however if you look closely you will find the many ways in which RISC-V is different.

Truly, the specification is highly readable and the footnotes enjoyable. Having implemented multiple MIPS cores and so far one RISC-V core, I'm deeply impressed with the care that went into the design.