Semiclassical quantization of chaotic classical system

So far in the introduction of quantum chaos, I have read that in the early day’s physicists quantized classically chaotic systems but could not find any signature of chaos in quantized systems. My question is why the absence of chaos in quantum systems was so obvious at that time, and what type of quantization rule they used, did they use the Gutzwiller trace formula to confirm that? Later after the advent of random matrix theory, people found the signature of chaos is there in the semiclassical energy levels, so previously why people missed these signatures of chaos while semiclassically quantizing a chaotic system?