After that, I'm guessing it was just fairly low priority to update a working system. Amazon's net income last quarter was >$20B. Saving millions is huge on the scale of one or two engineers spending a week tackling it, but it's too small for the organization to make it a big initiative. By the time engineers decided to update it, decision models like Jev were popular and are naturally a better fit for the task than an LLM.
If you think the former is a likely hypothesis, then why did you even click on TFA?
As for your question, seeing what others are doing helps one decide both what to do and what not to do.