Intel customers required a second source supplier, i.e. IBM, thus, AMD was providing that for Intel in the beginning. Then later on AMD created the x86 64bit commands, which Intel adopted from AMD so now both share the same ISA.
The licensing deals that legitimized AMD's unlicensed clones came later.
Customer needs don't really matter in cases where monopolist (ab)uses the law to kill competition. That's the MAIN reason why monopolies are problematic.