"This is especially true when all online job postings are online" -- as that true by definition, you probably mean "when all jobs are posted in public". That however appears not to be the case, by a long shot. From my vantage point it looks like employers at least in "tech" try to first use "networking", and only go to public channels when this doesn't yield. Often you have "stealth req" - "we have a candidate" - "create public req" - "oops we already found a match". Hence the name "LinkedIn" - it's meant quite literally.

Unfortunately that is very true and good point. I work for a newspaper company and was baffled during a conversation with the Classifieds-Jobs manager when she told me something to the tune of "95% of job openings are posted online, but 75% of the postings are fulfilled by internal networking, not by respondents to the job listing."

The adult generations have complained of the lack of virtue in their 1-2 successor generations probably for the past few millennia (in European history, going back at least to ancient Greek/Roman times) - enough written evidence has survived the times. What is qualitatively different from the "usual" stereotypes with this complaint here is the alleged deficits in face-to-face communication. But I agree with the caveat of lacking evidence.

OTOH, among (supposed?) adults, with the widespread use of email and "digital media" I have been observing an apparent decline in the quality of written work and correspondence (and I'm not (just) talking about rudeness and lack of etiquette in email), and also a lack of attention to refinement in oral communication, at least in business. But maybe this is just an instance of the stereotyped perception of a general decline in standards of excellence (and aspiration).