I occasionally receive contact messages from either ancestry or genes. I do try to reply straightaway but sometimes, if I get in from work and have brought stuff home with me to work on, or dog needs walking, contracts to do for the band I work for or tea needs making, I will put the email to one side to reply to proprly, later. Unfortunately, I will admit, sometimes that takes longer than I would ideally like it to. I keep the emails as 'new' and even forward them to myself, to keep them in the mailbox - i get round to them all eventually but, the more involved the enquiry, the longer it takes me to reply.
I think that is probably often the case - people begin researching, their trees go up on the web (via genes or whatever) but circs change - priorities change - I don't think people are being rude deliberately. It can be frustrating but i try not to take it personally when it happens to me, because I know i am not entirely innocent myself