Traditional marketing channels (meaning TV, radio, billboards, and even digital banners in some cases) are tightly controlled. If a newspaper in UK shows ads for a casino that isn't licensed in the UK, they can get hefty fines.
Many of the biggest online casinos are licensed where they are required to be, which enables them to market through any channel. Obtaining such licenses is costly and onerous, which is why many don't and instead operate offshore (licensed in Malta, Curaçao, Kahnawake, and so on).
If you have an offshore license, you are essentially limited to affiliate marketing and some banner ads on websites that aren't controlled much (or ones that lack internal checks). Affiliates can range from websites that review casinos and promote campaigns to social media (including Twitch/Kick streamers).
So if you're interested in non-affiliate marketing for gambling, you are limited to working with casinos that have all the necessary local licenses.
