It’s likely due to the Statute of Secrecy.
The wizarding world’s most severe laws are the ones surrounding the Statute of Secrecy. Since wizards internationally went into hiding, the most important wizarding law has been to keep magic secret from the Muggles. Each country’s wizarding government is held responsible for upholding the Statute within their own borders, and if they fail to, they can be punished by the International Confederation of Wizards.
“Adequate security measures were not enforced until the International Statute of Wizarding Secrecy of 1692 made every Ministry of Magic directly responsible for the consequences of magical sports played within their territories.”
- Quidditch Through the Ages
Each individual Ministry is held responsible for ensuring that Muggles aren’t exposed to magic, and must keep anything magical hidden, or be punished by the International Confederation of Wizards.
“In 1750, Clause 73 was inserted in the International Code of Wizarding Secrecy, to which wizard ministries worldwide conform today:
Each wizarding governing body will be responsible for the concealment, care, and control of all magical beasts, beings, and spirits dwelling within its territory’s borders. Should any such creature cause harm to, or draw the notice of, the Muggle community, that nation’s wizarding governing body will be subject to discipline by the International Confederation of Wizards.”
Fantastic Beasts and Where to Find Them
Because of this, the Ministries all try to avoid having anyone in the population they govern cause a violation of the Statute, which is almost certainly the reason behind the wizarding world’s strict laws. As an example, Rappaport’s Law was directly created as a result of a violation of the Statute of Secrecy.
In 1790, the fifteenth President of MACUSA, Emily Rappaport, instituted a law designed to create total segregation of the wizarding and No-Maj communities. This followed one of the most serious breaches of the International Statute of Secrecy, leading to a humiliating censure of MACUSA by the International Confederation of Wizards.
- Rappaport’s Law (Pottermore)
It was a very strictly enforced law, with harsh penalties for breaking it.
Rappaport’s Law enforced strict segregation between the No-Maj and wizarding communities. Wizards were no longer allowed to befriend or marry No-Majs. Penalties for fraternising with No-Majs were harsh. Communication with No-Majs was limited to that necessary to perform daily activities.
- Rappaport’s Law (Pottermore)
This particular law is a direct result of a violation of the Statute, and was a very significant law in American wizarding society. American wizards lived under stricter rules and more government supervision than those in other countries, because of this law protecting the Statute.
One of the most significant American magical laws was created in 1790, when MACUSA approved an edict to enforce total segregation of the wizarding and No-Maj communities. Rappaport’s Law, named after then-President Emily Rappaport, was created as a result of one of the worst breaches of the International Statute of Secrecy ever known, a breach in which the daughter of Rappaport’s Keeper of Treasure and Dragots and a Scourer descendant almost exposed the existence of magic worldwide. With the passing of Rappaport’s Law, intermarriage and even friendship between wizards and No-Majs became illegal in the United States.
- The Magical Congress of the United States of America (MACUSA) (Pottermore)
It seems very likely that similarly, the strict laws made by other wizarding governments were to prevent their populations from violating the Statute, though their laws weren’t quite as strict as those in America. It’s made clear that wizarding governments prioritize maintaining the Statute over everything else, including the rights of the wizards they govern.
