[求助]请教定语从句引导词who和that的用法

我看白勇语法上说修饰人who和that都可以啊。但我看到OG11th的130题

As a result of medical advances, many people that might at one time have died as children of such infections as diphtheria, pneumonia, or rheumatic fever now live well into old age.

OG答案讲解中有一句原话：The pronoun who, rather than that, should be used to refer to people.

那么请教这个此处为什么不能用that吗？who比that是不是只是一个Effectiveness的错误呢？只是一个更优的选择而已？

虽然很多情况下会毫不犹豫选择who在定语从句做关系代词指代人，但手边的书上确实没有看到that和who指代人谁更优先。不知是不是由于做主格只能选who呢？不知哪位NN可以找到个权威的说法。。。

呵呵，多谢几位啦！

LS说得好，反正还是以OG为标准，总不会错咯