First off, let me confirm that this text accurately describes the reality.
Second, this is less far afield from the common law than you would think. If you are in a jurisdiction without any binding case law on a particular point, a so called "question of first impression", you then turn to persuasive authority.
Persuasive authority includes case law that is binding in some other jurisdiction and legal scholarship, often in the form of a treatise or commentary. And, it is much easier to find an answer in a treatise which is carefully arranged on a subject matter basis, than to do case law research from other jurisdictions. This is particularly true when you have not devoted a lot of time to learning how to find the needle of the law you want in the haystack of the mountain of decided cases on all available subject.
The very difficult task of case law research was only possible on more than an isolated hit or miss basis at all in common law systems where case law matters in the years before the 1980s when computerized case law word searching started to become possible at an affordable to lawyers price, because a lot of full time institutional actors devote a great deal of time and money to developing and maintaining tools like digests, citation indexes, and annotations to statutes to allow practitioners to locate that case law.
If court decisions don't serve as binding precedents, those institutions aren't developed. For example, in common law countries, until very recently, there were no good resources for locating trial court decisions and rulings in state courts which handle the bulk of litigation, but whose rulings are not binding precedents. (Electronic record keeping in trial courts has changed the economics of this practice and made it much more common to publish trial court decisions and to index them appropriately.)
So, if persuasive authority in your legal system in the form of non-binding case law is hard to find because it wasn't worth the money for the legal system to collectively develop the resources to publish and index it on a systematic basis for an audience of pretty much the entire legal profession, the other form of persuasive authority, legal treatises, becomes much more influential by default.
You see something similar in very early legal opinion writing by American judges before the institutions necessary to systemically utilize case law precedents was developed. Judges were constantly citing treatises like Blackstone, which is something they rarely do now, because that was what was on their bookshelf.
Further, there are feedback effects. Smart people who wish to influence the law for society without going the legislative route in common law countries will often seek careers as judges. But, absent the psychic perk of influencing the law and making a difference in society, a lot of the most ambitious people in the judiciary in a common law system will choose instead to go the route of academia and seek to become law professors where they can have a similar influence, while earning similar pay and having more time off and freedom to pursue your own personal and professional interests.
So, in systems where legal precedents aren't binding, people who might otherwise be inclined to write probing legal opinions that develop legal concepts are less inclined to become judges, and the people who do become judges care more about getting the right result and less about explaining their decisions in a way that will influence future judges in the same circumstances.
Finally, consider that many civil law legal systems involve countries with a lot less appellate litigation than the United States (currently 330 million people with more than 200 years of case law), or the UK (currently 60 million people with about 1000 years of case law), or India (more than 1 billion people with a couple of centuries of case law, since colonial precedents have relevance).
Suppose that you live in Denmark or Belgium or Portugal or Costa Rica or South Korea, where your population is much lower and your time frame during which your legal system has been in place is not as long.
In a situation like that, half a dozen or a dozen leading legal scholars can publish treatises over ten or twenty years that are going to cover, somewhere, the lion's share of the pressing issues in the legal system, and there is probably only one law school in the entire country, so it is quite likely that most of the lawyers in the entire country took contracts or property or family law from the the same people in law school, which makes them predisposed to consider a treatise written by that professor a credible one in that area of law. And, all other sources are a comparative vacuum.
If you are a judge, why cite non-binding precedents from your fellow non-specialist judge in a country that simply has no precedents in many areas of law and has fewer carefully reasoned ones, when you could instead look for guidance from the person who taught you this area of law in the first place and literally "wrote the book" and who was probably consulted by the government in any recent amendments to relevant civil code or statute of broad general applicability. And, once you start out using those methods, it becomes habitual and legal treatises become very influential.
