语法就是这么规定的：
由more than one (或more than one + 单数名词),many a + 单数名词作主语,谓语动词要用单数形式.例如：
1）More than one student has passed the examination.
2）Many a boy learns to swim before he can read.
注：如果more than后面是复数名词,则谓语动词要用复数.
more + 复名+ than one "接复数谓语.e.g.
②More students than one have been there .不止一个学生去过那儿.
参考文献：薄冰实用英语语法详解连载之二十《一致关系》