This could be very true, but to show the causality it is necessary that tree shaking abilities of language/tools on average precedes widespread use of huge depe

This could be very true, but to show the causality it is necessary that tree shaking abilities of language/tools on average precedes widespread use of huge dependency trees. It could be in reverse. That is when for some unknown reasons multiple dependencies appears, tree-shaking tools follow and it is just easier to create them for static languages.