Why do marketers prefer paid search in SEO rather than organic search which is free?

Because it is easier to obtain. Pay big bucks and have your ad on top. Organic you pay big bucks and your site is at the top.

The difference?

Google Ads you have to pay big bucks every month and for organic, you pay big bucks for a few months then the cost goes down.

Organic ranks are much harder to do but produce better results because you also gain long-tail rankings.