Email threads are useful for context. I much prefer having the email thread to understand what is being asked and why, rather than a lone email from someone (usually a PM or someone non-technical) that attempts to paraphrase the ask--poorly--and gives me a nonsensical request: "AA, please tune the turbo encabulator."

But it's also really helpful when someone at least summarize or reiterates the specific ask to me at the top of the email thread, rather than just CC'ing me on a reply with "+AA". That seems to be more what the author's complaint is about.