Thanks for the suggestion. DreamHost takes security very seriously and that’s why a lot of security processes are indeed free. You may not notice but all DreamHost-hosted sites enjoy WAF firewall protection, with automated rules blocking attempts like brute-force login to sites and more. You may want to read this interview to our security team.
Even the malware scanner you mention is free to some extent: it’s used by some of the automated services that DreamHost team runs regularly. And, in case your site gets vandalized, the Support team will run the malware removal tool at no extra cost for you for that incident.
The team worked hard to make the tool affordable compared to its utility. At the moment there are no plans to change the pricing scheme.