1) Prevent war between 'gorillas'. All of them were putting major resources into R&D in hardware and FRAND patents allow them to share knowledge without heavy fighting of negotiations which would only filled lawyers pockets
2) Lower barriers for small players. With FRAND they can license necessary technology without breaking budget and allow to concentrate on product.
Now we have third situation: gorilla enters the fray and want to use FRAND system without paying entry fee (resources put into R&D). It is Apple which abuses FRAND system, not Motorola, Nokia, etc. If it wants to not be treated with contempt it should put their 'design patents' into FRAND pool.