It starts with people who feel they’ve got more to lose (like those supporting a family) working extra to avoid looking like a low performer, whether that fear is reasonable or not. People aren’t perfectly rational, and job-loss anxiety makes them push harder than they otherwise would. Especially now, when "pushing harder" might just mean sending chat messages to claude during your personal time.
Totally anecdotal (strike 1), and I'm at a FAANG which is definitely not the median tech job (strike 2), but it’s become pretty normal for me to come back Monday to a pile of messages sent by peers over the weekend. A couple years ago even that was extremely unusual; even if people were working on the weekend they at least kept up a facade that they weren't.