Humans absolutely are not built for large social networks. There is a theory called Dunbar's number that suggests that humans have a cognitive limit of ~150 social relationships.
IMO, the continuation to Dunbar's number (theory) is Yuval Noah Harari's theory, as outlined in Sapiens.
That is, early humans were intelligent animals, but limited in our sophistication by Dunbar's number, so to speak. That is our range of social behaviour (and therefore most behaviour) was biologically limited to small social groups.
The Palaeolithic revolution circa 50kya-100kya was (according to YNH) the invention of language and "fiction" sophistication which enabled cooperation and in larger groups. The concept of a "tribe" with ancestors, shared traditions and social cooperation in much larger groups. Much larger groups allow for much more sophistication.
In some sense, he defines human progress as the quality of cooperation in larger groups. Basically culture takes over from biology, in determining effective human social group size.
Social networks are just another advancement in this trend. All these advancements are somewhat pathological, because they're at odds with our innate (noncultural) limitations. Consider how bad we are at "politics" and how "politics" is a bad word. The contrast is decision making in small, tight knit groups.
https://en.wikipedia.org/wiki/Dunbar%27s_number