Addressing this again :-
Blizzard cannot control what is happening outside of the game. If you’re concerned about websites selling illegal services, you may report these via the usual hacks@blizzard.com email. However removing external websites/adverts is not an easy or fast process.
For ingame advertising, we have our support article about it here (note that accounts that are found to be used purely for advertising will be closed permanently)
The ingame “report group for…” → “Advertising” absolutely does work and leads to accounts being actioned. The “Advertising” report was implemented for the very purpose of reporting these adverts in 2018, however as you say:
If players stop using it, then adverts will not be reported, and it will take longer for action to be taken on these accounts. Often they will be using multiple accounts for these adverts which is why you can see the adverts re-appearing later, and this is also why accounts that are used purely for advertising will be closed permanently.
The thread will be closed again because there really is nothing further that can be brought to the discussion here - continue to report the advertising in the LFG tool to us via the right click report option.
Thanks!