Corporate application general question

I am trying understand what mindset a corporate code writer would be in. For example why would you write code for one specific browser while your company uses several browsers that is unsupported for corporate functions.
Forms that a job critial that sections are missing where the code is being totally ignored. I remeber reading that you should check your code agianst many browsers standards. I am not understanding the depth of it becuase i find it frustrating learning a standard while real life it is punitive.