Somehow I don’t think that’s their primary concern at the moment

Granted. But it's going to be someone's concern after all this is over.

And unlike landmines, how do you detect and remove kilometers of cable?

Glass breaks down to sand so I wouldn’t worry too much about it

With physical weathering.

I was about to respond to your comment above by saying landmines are 1000x worse, but you just said the opposite, which is completely incomprehensible to me. Are you perchance thinking of literally just the environment, not the fact that countless lives will be harmed and lost for decades to come because of the indiscriminate nature of landmines?

While landmines have the obvious explosive and shrapnel first order effect of causing great harm, I'm wondering about the subtler effects of fiber optic cable pollution.

What happens when someone uses agricultural machinery on a field littered with cable, both to machinery and people? What are the consequences of consuming broken bits of cable that may mingle into produce?

And most critically, if the above are issues, how do you then remove cable from fields at scale? It would seem maddening to try to detect and gather kilometers of tangled glass.

If it had economic value people would find a way. But it doesn't. So.

At the extreme of 10KM range we are taking about 2.4kg of glass maximum. Spread of over 10km. It is largely insignificant.

Even if you had 100 drones starting from the same exact place and going to the exact same place you would find 24g of glass per meter. A single leftover beer bottle would be at least 6 times that amount.

When you worry about stuff it is useful to do the work.