Because they can read your emails without opening them...or they've cut to the chase, looked at your profile, have no interest in you, and deleted your email.
So, do yourself a favor; Make sure that your profile is well-developed, clear, polite, and with proper grammar. Then, make sure you have good quality, non-bathroom/non-selfie photos, and then, stop emailing people, or at the most, only send emails to profiles that state an interest in SMs, and only those where you fit into their age range and any other descriptors they have in their profile, whether its race, cock size, or physical shape. Do not email people like you're a Value-Pak SM.
Develop your profile like you would a marketing piece. People who are interested will find you. This stuff takes time. If you're of the mindset that this kind of thing is always like an instant hot water dispenser, you'll be forever frustrated.
There's an area on the main Forums page, I think the header is Achieving Single Male Success, where you can create a new thread and ask for input on your profile. Be thick skinned. You'll get the good, bad, and Ugly...from the good, bad, and ugly, but these folks are dead-on.
Good luck and have fun,
BT
-Of course, all of this is just one man's opinion. As they say, opinions are like assholes. Everyone has one and some are more expressive than others.