Some potential reasons are you are in a competitive industry, you have other key phrases that have proven to convert, there's low search volume, and where you are searching (Google) from.
Sometimes the ROAS will plateau...
It is likely that LinkedIn campaigns to warm leads (aka remarketing) could be a good fit, but LinkedIn campaigns to cold leads is only a good fit for a few narrow industries.
2 Expanded Text Ads & 1 Responsive Search Ad.
To avoid limiting our ability to service the campaign. That means, our campaigns become more profitable as a percentage as you grow.
It's possible to target competitors beyond the basic competitor campaign (which is where we show an ad after someone searches for a competitor). We can do this using affinity & intent audiences (which are audiences of people who are frequently associated with the competitor's business).
We use SEO tools and craft a keyword strategy. Then we calculate the total amount of monthly leads/sales and cost-per-lead/sale using the formula on this post.
Doing this causes the algorithm to not be able to spend the full budget, and ultimately, causes us to fall behind spend and lose valuable time in the learning process, too.