“Euphemisms such as “sagi nahar” have fallen out of use – that’s not an answer.”
Some have, some havent.
We may not refer to a Sagi nahor but I have heard many people refer to a “bais hachaim”
I have also heard some people refer to cancer as yehne machla, as It seems you have as well.
I’m not saying I avoid the word cancer, im not saying it is halacha in shulchan aruch or that saying it leads to bad things. Im not even saying that it is a good reason or that it makes sense.
You wanted to know why some people avoid saying it. Now you know.