Because glyphosphate is almost certainly toxic. We have evidence for that. (Roundup is more toxic than glyphosphate alone [1].)
That doesn't mean it's carcinogenic in a colloquial sense--we don't have evidence for that, again, beyond the carcinogenic capacity of commonly-eaten foods.
https://www.nytimes.com/2017/08/01/business/monsantos-sway-o...
Then why has Monsanto settled one hundred thousand claims and paid ten billion dollars in judgements against them and settlements?
Then why was a top official at the EPA emailing Monsanto executives saying he should "get a medal" if he was able to kill the CDC's study?
https://www.npr.org/sections/thesalt/2017/03/15/520250505/em...