To take a facetious example, suppose I broke 300 random pixels of a 1000x1000 LCD display that cost $100.
On visual rough intuition, it's seems clear that less than 1% of the screen is broken, it intuitively would seem absurd to toss the LCD screen versus fix it. But automated manufacturing technology is so good that it really doesn't cost a lot to make a totally new one.
On the other hand, your time is relatively valuable, as are some replacement parts. Suppose you spend 10 hours ordering parts, soldering wires, debugging, testing, etc to get it to fully functional. Why not spend a fraction of that time at work, and another fraction of time volunteering at park cleanups or buying carbon offsets?
The numbers above may be off in one way or another, and depends on the product, your pay, and belief of environmental impact of things like throwing stuff away vs volunteering / carbon offsets.
But one point seems clear to me -- which is that if I broke what visually seems like 10% of a $100 product, the fully-burdened real economic and environmental cost is a lot more than $10 to repair it. And the lynchpin is the automated production makes new stuff relatively cheap.