And likewise it's unethical for a candidate to attend an interview if they have no intention of considering a potential offer.
I'm currently happy at my job, and don't think I'd like to consider another job any time soon. However, historically, in previous jobs, I usually don't notice that I want to move on, until it's too late, and I'm too burnt out to do well in interviews. It's been recommended to me, by multiple people to interview frequently, even if not interested in changing jobs, to get some practice in. But doing that feels unethical. I frequently consider it, but have never done it because it feels dishonest and unfair.
But then by the time I want to change jobs I'll be burnt out, and and out of practice interviewing, creating a very depressive loop of failing at job interviews, depressing me further.