参加接力赛 为什么是 join the relay race 而不是 join in the relay race？

参加接力赛 为什么是 join the relay race 而不是 join in the relay race？

当join的意思是参加的时候，接宾语时不加介词，直接join something, 如 join the relay race参加接力赛，let me join you, 让我跟你们一起吧 等等。
没有宾语时用join in，如 I joined in and sang along 我加入了，一起唱歌 （我跟着一起唱起来好像更通顺）
有具体的人或事作为宾语时不加in，就是这样
追问：通常情况下不是join in+活动，join+组织么？
追答：并没有听说这样的规则。下面是我从牛津字典里复制粘贴的，我觉得挺详细的，而且都有举例，join和join in的对比在第五项，所谓join+组织的意思在第四项里有解释。所以说，join in通常暗含了加入对象是活动，但是这是个语义的问题，而宾语前加不加介词这是个语法的问题。
join |join|

verb [ with obj. ]

link; connect: the tap was joined to a pipe | join the paragraphs together.

• become linked or connected to: where the River Drave joins the Danube.

• connect (points) with a line: join up the points in a different color.

• [ no obj. ] unite to form one entity or group: they joined up with local environmentalists | countries join together to abolish restrictions on trade.

• become a member or employee of: she joined the department last year.

• take part in: I joined the demonstration | [ no obj. ] : I joined in and sang along.

• [ no obj. ] (join up) become a member of the armed forces: her brothers joined up in 1914.

• come into the company of: after the show we were joined by Jessica's sister.

• support (someone) in an activity: I am sure you will join me in wishing him every success.