Because claims that one singular concept or idea can explain pretty much everything in life have, historically, been quite false. Worse, such claims tend to attract people who like to have one simple solution for everything, or like to have one single thing that's root of all evil, or like to have one simple explanation for everything, etc. The damage such people can incur, especially when equipped with a grandiose enough concept, have (again, historically) been quite incredible.
Indeed! Reaching the critical mass in a nuclear reaction pushes things apart, while reaching the critical mass in a social movement helps pull even.more participants.
Is there not a value in drawing interdisciplinary ties between fields? Physics underpins reality, would it not be feasible that it's laws scale to higher order complexities?