It is first important to understand what is negative on the 10 yr treasury. The coupon rate is not negative. The yield is negative.
There is a huge difference.
This is supply and demand. If the coupon rate is set and people are willing to get a negative yield that is due to so many people bidding up the price and driving down the yield.
Here is an explanation
Bond Yield Rate vs. Coupon Rate: An Overview
A bond's coupon rate is the rate of interest it pays annually, while its yield is the rate of return it generates. A bond's coupon rate is expressed as a percentage of its par value. The par value is simply the face value of the bond or the value of the bond as stated by the issuing entity. Thus, a $1,000 bond with a coupon rate of 6% pays $60 in interest annually and a $2,000 bond with a coupon rate of 6% pays $120 in interest annually.
I hope that helps.
https://www.investopedia.com/ask/answers/051215/what-difference-between-bonds-yield-rate-and-its-coupon-rate.asp
“ It is first important to understand what is negative on the 10 yr treasury. The coupon rate is not negative. The yield is negative.”
Unlike a handful of EU countries (Germany being one) neither the yield nor the coupon on the 10 treasury is negative. Nor is it negative on any other US debt.