Help me understand this

I've always heard that exercise helps with insomnia as physical activity tires the body so we can sleep better, right? Then why does it have an opposite effect on me?

The night before I managed to get almost 5 hours of straight sleep unaided which was a rare thing for me since my severe insomnia started almost a year ago. But last night after doing 2 hours of cardio, 4 hours before bed time, I fell asleep at my usual time at 11 pm, then woke up 2 hours later at 1 am. Very frustrating how exercise worsened my sleep maintenance insomnia rather than helped it.