united-states
In the United States, both among practicing lawyers, and in the academic field, disciplinary boundaries are very loose. Looking only for "contract theory" would miss much of what is going on.
Lawyers who practice primarily in the area of pre-litigation contract law are called "transactional lawyers". Transactional lawyers have the same professional license as lawyers who engaged primarily in litigation, or lawyers who do both, but they choose to take on work of that type. Frequently transactional lawyers specialize even further. One lawyer might do primarily residential real estate closings. Another might handle mostly commercial real estate closings. A third might handle real estate development and construction law. A fourth might handle mergers and acquisitions. Another might handle mostly banking contracts. Another might mostly deal with insurance contracts. Another might handle mostly estate planning. A different lawyer might focus on condominiums and home owner's associations. Other lawyers focus mostly on oil and gas transactions.
In general, practicing lawyers are much more likely to focus on a particular kind of contract than on contract design generally.
This is also true in academia, although academics tend to examine issues at a somewhat greater level of generality than practicing lawyers.
In academia, in law schools, there are lawyers who focus heavily on studying contract law. There is even a contract law professor's blog. Many professors who study contract design at both the law school level and in undergraduate business schools identify instead as business law professors.
Other professors who specialize in contract design focus on only particular kinds of contracts, such as agricultural law and taxation, merger and acquisition contracts, securities law, real estate financing, marijuana business law, international trade law, and international finance law. Contract design in all of these fields is also pervasively influenced by tax law - with undergraduate tax law in accounting programs tending to be more focused on compliance and law school tax law more focused on transaction design.
Economists also study contract design. One of the main issues explored by economists is the question of under what circumstances it is better to structure economic activity within a single business raising issues such as the "theory of the firm" and agency problems, on one hand, or to structure economic transaction instead through contracts between multiple firms.
Both legal scholarship and economic scholarship tend to be weak in what I call "descriptive economics" which is the study of what contracts and transaction structures are commonly used in real life to deal with particular kinds of situations.
In short, the subjects about which you express interest are studied, but professionally, study of these subjects is highly fractured.
