If doctors are "unsure" of a link between cancer and cell phone, why are there not warnings "cell phone use may be dangerous to health"?

Life is risky: Everything on planet Earth causes cancer. Actually, everything outside our planet also causes cancer. Therefore, the whole world would have to be like California, where we have a cancer warning sign on every building I have ever been in. The result is that nobody pays attention to those signs. So, to truly warn people, we can only put signs on the most dangerous things, which excludes cellphones.

There would need to : be more evidence for cancer in humans. Cell phone radiation is low-frequency & low energy. It is actually nonionizing radiation. Unlike high frequency wave ionizing radiation, it is doubtful it can cause cancer in humans. Cell phone radiation was however, shown to ^ risk for developing schwannomas in rats & gliomas in other animal studies. REF: https://www.mskcc.org/blog/do-cell-phones-cause