"I am the law!" - The empirical link between lawyer-lawmakers and legal cost/burden
For better or worse, a large part of the politicians sitting in national/regional parliaments or similar positions of power are trained law professionals. As lawmakers, they have the unique opportunity to influence the amount of available work for their own profession (particularly if they don't intend to give up all legal practice when they are first elected). A hairdresser cannot mandate more haircuts, neither can a football club owner require people to go watch his team more often. But a lawyer-lawmaker has the opportunity to influence all kinds of policies in order to both (i) limit the competition within his profession (e.g. by requiring a notary to be present for various transactions, controlling the stringency of the bar exam etc.) and (ii) increase the demand for legal services (e.g. through regulations with high compliance costs, and generally increasing the number of regulations).
It would be interesting to examine this issue empirically, e.g. by comparing legislative outcomes in settings where more participating lawmakers have a potential personal business interests to outcomes where this is not the case.
Some food for thought, though (to my knowledge) not linked directly to national legislation: Why do more than 80% of candidates pass all steps of the medical exam on the first attempt (https://www.usmle.org/performance-data/), while first-attempt pass rates for the bar exam are much lower (<50% in some states - https://lawschooli.com/bar-exam-pass-rate-by-state/). Is it harder to be a lawyer than to be a doctor? Or is the industry more interested/successful in limiting competition than the medical profession?