I also had never experienced runner's high until I added extremely light runs. My regular runs would usually leave me tired so I thought that I didn't experience them like other people. I don't remember exactly why, I think it was I need to hit a higher mileage threshold, so I started trying to get any extra miles in anytime I could, including a light jog anywhere I needed to go. That's when I finally experienced it. For me, key to the runner's high was the runs that got my heart rate into zone 2-3 (approx. 60-75% max HR) but importantly weren't long runs which would tire me out. Tiredness is a big trigger for me to feel shitty so I think that's why I never had the feel goods after the runs.
Reading the picture from right to left makes it so satisfying.