Why are my answers deleted?

Question

Why are almost all my answers deleted?

For example, I was helping this person to resolve his issue and now it seems I would need to write the whole thing all over again:

https://www.c-sharpcorner.com/forums/how-to-export-in-excel

 

Anyway, I'm trying to follow the guidelines, have I done something wrong?

I did suggest some external libraries with which I'm familiar, but I have also provided a solution without it.

 

Nevertheless, I did see that others have suggested external libraries as well so I don't know if that is the problem?

If it is, then why are other answers not deleted as well?