Garmin, why don't you fix accuracy of intensity minutes?

It's working fine for me. Assume you've already looked at online support?

Venu - Improving the Accuracy of Intensity Minutes and Calories (garmin.com)

How Are Intensity Minutes Earned? | Garmin Customer Support

Venu - Earning Intensity Minutes (garmin.com)

In what way are they not accurate? Intensity minutes is based on your heart rate. Is your heart rate accurate?

I have 65 min of moderate to intense exercise in 3 sets and it registered 26 minutes. 

They were accurate in the past, but not recently.  I have looked online and tried resetting the zones. I do not sleep with my watch.

And the heart rate was elevated enough? Easiest is probably that you post a link to the activity. We also need to know your resting heart rate and the watch model.

That you do not sleep with the watch will probably make it harder to earn intensity minutes since your resting heart rate will be higher.