It's about keeping radio time to a minimum and avoiding unnecessary information. The "position" in the "pass your message" reply is not a complete position report. No need to specify the time, the ATS unit knows what the current time is. She will have a general idea of your routing by knowing your destination; if you're planning something a little unusual it doesn't hurt to mention your next turning point but if she needs to know, she'll ask.
Most of that position reporting stuff is intended for things like long oceanic or desert flights where your information may need to be relayed by an airliner or something, and it would be important to know what time the original message was sent and when the next one can be expected.