What ads before logon are you referring to? In the screen shot below, there are two that I see. The box in the middle right side and the one at the bottom. Neither appear offensive but there may be others I haven't seen.
I suspect the web site owners subscribe to some type of advertising service and have no control over the ads presented. The advertising technology is so intertwined with internet activity such that ads are tailored for you based on your history using a web browser, Google, Siri, Alexa, and more.
Like BB_TX, I stay logged on all the time and I use Adblock Plus. I never see ads. Brave and Duck Duck Go are other alternative but do your research before you go.