Microsoft Outlook: team members can decline your request if you have a vacation

I don’t understand why a lot of team members like to send to people with Accept, Tentative or Decline request via Microsoft Outlook if they have a vacation. Don’t they forget that we have the right to decline their request ?  

The best way is to uncheck the Request Responses option and just inform them (No response required). J

 I don’t understand why a lot of team members (even program managers) still reply to the old email thread some people have already discussed.  Don’t they forget that they can use “Show as Conversations” function in MS outlook? They will never miss any conversation.