Because 能不能引导主语从句

ecause不能引导主语从名,只能引导状语从句.这个句子就是just because you've been working in a field for many yearthat does't mean u have to turn that parrern ……

很少见，至少我没见过
不过从这个句子看来也只能分析成主语从句了

because是不能引导主语从句的，这一点是肯定的。
其次呢，这句话确实有错误，如果想表达同样的意思可以说成：It's true that you've been working in a field for many years, but it doesn't mean you have to...
虽然改动有些大，但是应该还是比较符合英语习惯的，原来的那句话感觉好像是从中文语感...