Remember, "Bulk delivery" keeps lots of people working! Paper mills, ink makers, printers, bindery, companies that hire people to stuff envelopes, and of course, the postal sorting facilities, truck drivers, clerks, and letter carriers. In addition, trucking companies, fuel centers, and other assorted folks.
The benefit of "junk mail" is that it is not intrusive! You can deal with it at your discretion. Unlike telephone solicitors, who bother you at dinner time, junk mail just sits on the counter, table or wherever until you pick it up!
Besides, "junk mail" doesn't get forwarded. Only first and second class mail gets forwarded. Junk mailers may post address correction requested on any piece of mail. Doing so, the post office will provide them with the new address, for a fee. Most junk mailers don't wish to pay the fee, hence the mail doesn't follow you. However, creditors get mighty unhappy if their mail is not forwarded! And the consumer gets to pay the late fees, because it is our responsibility to update our address.