Why Do People Prefer Ajax Apps Over Java Applets?

From the common user perspective (like my grandma), why would they care
if its a java applet or an ajax application? Say I want to make a chat
system on my website...If i'm doing really involved Comet push-style
data communication, and rendering everything using DHTML, why would
users prefer that over a java applet?

Moreover, say I use a java applet to transfer data through a socket
connection, then use DHTML to display the data, so that basically the
front end is the same, but the backend is differs, why would a user
prefer the comet-style programming over applet?

I'm asking because I wrote an Ajax chat system through polling, and I
want to switch to a Comet push-style system because polling just isn't
responsive enough. I want to know if I can avoid Comet (since it is
alot of overhead for the server) and just use an applet in the
background to transfer data through socket connections, then use DHTML
to render the chat boxes.