It might appear unethical to members here but it is not illegal. Their advertising team must have coordinated well with the legal team before deciding keywords.
There is no such rule restricting the usage of the keywords but you only have to pay for your ads to be shown if you have categorised under that category so whenever some user input the keywords in search bar the ads will be displayed to him if he/she has not enabled ad blockers.But if Binance is trying to attract people with such keywords then it's cheap tactics as they don't have any link up with forum and they are doing it for personal profits only which is unethical.
Today I saw the ad again. It's starting to be more regular, even though it only appears very punctually.
I don't know why others are not able to see that particular advertisement from Binance in your region or any other one and you are seeing it on regular basis? Have you tried it on any other device and still seeing that particular ad?