Spam is the evolution of cold-calling and tele-marketing. I believe it’s as simple as that.
In ye olden days (The 80s and early 90s to me!), the pre-internet era as it were, saw ‘spam’ take the form of people knocking on doors to try and sell you various wares. It also saw you receive random phone calls, from people trying to sell you stuff. You might also get leaflets through the door. Basically, all of this was a string of unsolicited efforts to flog you things, and in some cases, I believe to scam you out of your hard-earned cash.
Nowadays, spam takes two primary forms. Phone calls continue, and if anything, they are perhaps more frequent. Fortunately, mobile phones often have apps that enable call-blocking and spam filtration, not that this deters these spammers and scammers.
The second method is via email. Such is the frequency of spam emails that most email providers now give you a spam folder. Be it personal email, or work email, those folders are usually very busy.
What is the end-goal of all this junk correspondence? I would wager it boils down to money. In fact, I am certain of it. Be it pedalling products, or deceiving people through cruel, opportunistic schemes, spam is about money. It is an unfortunate element of human nature, one seen throughout all our history, that some will try to con others out of their money, or more.