Writing a compiler seems like a much harder problem than an interpreter. If that is so, why was the first compiler written six years before the first interpreter?

Both were introduced three years ago as a part of a two-tier compiler system. Ignition is a bytecode interpreter whose job is to start executing the JavaScript with as little delay as possible.

Apple integrates LLVM compiler to boost WebKit JavaScript performance Since compilers already make fast code, why not take advantage?