Why jobs lost when after reconnect ssh?

I have a job that runs in the background via ctrl + z and bg, and after reconnecting ssh I cannot find that job in the jobs command but can find it in ps grep. For now, I searched this and I get the tmux may be a better solution, however， I am still wondering why exit ssh will lose jobs in the jobs command. I've put that in the background, it should exist after reconnecting, Am I right? https://unix.stackexchange.com/questions/29692/how-can-i-manage-jobs-after-i-disconnect-from-my-tty-ssh-session