Marketing != advertising. I think you mean the latter!
Not much to add to the excellent points of @Rat_au_van and @Stewart earlier! Different companies have different user acquisition and retention models. CFD firms, such as the above, operate, from a marketer’s standpoint, a quick churn and burn model.
As Adam put it:
See the disclaimer on any CFD site:
When a company stands to gain thousands of pounds during a short customer lifecycle, it makes sense to invest a lot into advertising, which is a higher CAC (customer acquisition cost) channel.
Meanwhile, we are a tech startup operating a freemium model. We optimise for our customers to enjoy and benefit from the product, and stay with us for decades. The most scalable, efficient channels for us are organic, the same channels most successful tech companies such as Airbnb, Lyft, Pinterest, etc pursued during their early stages.
Again, different companies have different models. Booking.com is famous for its enormous spending on (performance and display) advertising, and how deeply they optimised it. Grammarly is another fantastic company with a large and deeply sophisticated advertising effort. In later stages, when you try to reach the mass market, it also makes sense to advertise - Monzo is a great example.