Delivery reports are a convenience feature that lets the sender know if the message they sent has been received (not read) by the recipient's device (for this, it has to be online and have sufficient storage space, though modern phones usually have so much storage the latter is no problem at all).
Every single phone I ever had, from early Nokias in the 00s to Androids and iPhones, had it disabled by default. While feature phones often delivered these reports with a pop-up and sometimes notification sound, which some people could deem annoying, this trend continues even with smartphones, which typically display it merely as an indicator in the chats list of your messaging application.
So, is there an actual reason why it's turned off by default everywhere? The feature has to be enabled on the sender's device to receive these and the recipient has no way of opting out of this, so it's not a privacy thing by any means.
UPD: Apparently, carriers in some countries charge customers for receiving delivery reports as if they were sent messages. I've never realized this - reports always were absolutely free where I live. Thank you for your responses!
I do understand your point, however, the reality sucks and you're sounding like not trying to do anything about it is the only possibly right thing to do. I certainly don't feel like living in an infospace consisting of 90% of ads and possibly-maybe 10% of actually useful information