They don't need to be that way but by a certain point they g

They don't need to be that way 他们不是必须那样
but by a certain point they get so但当他们那样达到某个阶段时
they can hardly change it 他们很难改变了
get so 指代 be that way.
整个句子是but连接的并列句.
后半句是个主从复合句结构,they can hardly change it 是主句,
by a certain point they get so是时间状语从句,
其中 by a certain point 可以理解为 they get so 的时间状语,
也可以理解为they get so 是 a certain point 的定语,类似的结构例如：
by the time I finished the book,
the instant she woke up
这部分更中规中矩的结构是：
they can hardly change it when they get so by a certain point