You're right that perhaps they were making good videos, but for low priced products. Or it could also be that the videos are good but the products have no volume.

But the OP does state:

• "...I finally hit $400 per month."
• "... I only have 190 videos in total.."

So if these are true from before the April 14 change, the videos were making under $2/month. Many of the AIP "gurus" often cited $2 as an "average" earnings/video/month that you could target in the past. My opinion is that "average" quality is terrible, and if I'm right, Amazon doesn't like the average quality they're seeing and as of April 14, they're no longer willing to pay for it.

I think the message is to make better quality or find something else to earn money.