Why do software companies struggle to support their code documentation?

I worked with a couple different software companies and one thing in common is that both companies don't prioritize writing code documentation at all. I asked around, and many developers from other companies shared the same issue. Any bit they write is in a seperate application which often gets out of date or forgotten. This often leads us developers to not understand code easily and new developer onboarding really slows down.

I have been researching quite a bit on why this is an issue among so many companies. Many approach the clean code policy due to the pain in writing documentation but it does not help according to my survey. I came across so many software tools that somewhat automate documentation generation, draws chart from code etc. I really don't see many people talking about these. Why is that the case?

Is this a problem worth looking into or should developers not worry about improving documentation system and focus on other things? I really want to hear your opinion about it. Thank you.