Some commenters on my earlier post faulted Congress for restricting (though not banning) only picketing around national cemeteries, which as I understand it mostly limits the law to military funerals. Why doesn't it apply to "funerals of gays or 'normal people?'"

Because restricting noncommercial conduct around all funerals would be pretty clearly outside Congress's enumerated powers (even setting aside the First Amendment constraints on those powers). Even as to this law, there's some question whether Congress has the enumerated power to restrict noncommercial conduct on state-run streets outside federal cemeteries; but at least there Congress has a plausible case that such restrictions are necessary and proper to protecting activities that take place on federal property. (As to restrictions on picketing around military funerals, there's also a somewhat more far-fetched case that such restrictions are necessary and proper to helping raise armies.) But a restriction on all funeral picketing, with no connection to federal activities, would be pretty clearly unconstitutional.