Ah, you were so close...
If you actually read the article, you would find the selection criteria and the explanation for the criteria.
First, a preface.
The article was published in 2009. At the time, AstraZeneca, the maker of the controversial statin Rosuvastatin, had been engaged in a yearslong intensive campaign to promote the drug. The editor of The Lancet wrote "AstraZeneca's tactics in marketing its cholesterol-lowering drug, rosuvastatin, raise disturbing questions about how drugs enter clinical practice and what measures exist to protect patients from inadequately investigated medicines"; CEO Tom McKillop [1] angrily fired back. Consumer rights group Public Citizen tried to get the medicine withdrawn for safety reasons; the FDA denied the request [2.]
AstraZeneca prevailed, and Rosuvastatin proceeded to make billions of dollars a year in sales. Today, 42 million Americans take it and in 2015 it was the most prescribed branded drug in America.
Now, back to the article. Most new drugs focus on studying the most diseased patients first and then, if possible, attempt to expand to the (far larger and more lucrative) prevention markets later. Statins are no different. The overwhelming majority of research on statins has been industry-funded, done on patients with CVD. Pharma companies want to expand to a larger market, of course. So there are efforts on many fronts. One was to broaden the definition of CVD or other criteria for starting statins. For example, in 2017 the definition of high blood pressure was successfully changed from 140/90 to 130/80. That bumped up the proportion of US adults with CVD from 36% in 2011-2014 [3] to 48% in 2013-2016 [4], or in other words, added 30 million US adults to the market. Similarly, in 2013 the 2013 ACC/AHA guidelines encouraged starting statins for anyone with LDL-C ≥190 mg/dl "even in the absence of other risk factors" which increased statin use from 31 million to 92 million Americans from 2008-09 to 2018-19 [5.]
Where did these changes come from, what motivated them? Studies, of course. Studies like the AstraZeneca-funded JUPITER trial, which claimed an improvement in the health of participants with even _low_ levels of LDL-C. A lot of this stuff was considered fairly strange, and it didn't seem to replicate. Thus the meta-analysis. Are statins truly useful for prevention?
So, in short: Most studies investigating statins in real depth are funded or influenced by industry. They usually focus on the sickest patients, presumably to get a larger effect size, yet the industry is constantly trying to prescribe to a wider audience - the healthier patients - often on grounds that mainstream health authorities find weak. This meta-analysis was only able to include 11 studies because industry SOP is to study the sickest patients yet prescribe to a wider audience. And as you might then expect: "This literature-based meta-analysis did not find evidence for the benefit of statin therapy on all-cause mortality in a high-risk primary prevention set-up."
[1] If the name sounds familiar, it's because Tom McKillop was the CEO of RBS who "aggressively" pursued leveraged buyouts up until its collapse and bailout in 2008.
[2] Here's the 10-year followup on that: https://www.bmj.com/content/350/bmj.h1388
[3] https://www.ahajournals.org/doi/epub/10.1161/CIR.00000000000... "total CVD prevalence, age >20y, both sexes" from Table 12-1 is 36%/92.1M
[4] https://www.ahajournals.org/doi/epub/10.1161/CIR.00000000000... "total CVD prevalence, age >20y, both sexes" from Table 13-1 is 48%/121.5M
[5] https://pmc.ncbi.nlm.nih.gov/articles/PMC10203693/