It looks like they did it on purpose. See https://clojure.atlassian.net/browse/CLJS-254 "throw error if multiple :require, :use, :require-macros, etc clauses".
That's not the only difference! For more, see the Namespaces part of the "Differences from Clojure" page, https://clojurescript.org/about/differences#_namespaces.
Anyway, the path of least resistance, when writing cljc files that should be portable, is to use ClojureScript's (more restrictive)
By the way, what do you like about multiple