Probably for the same reason the USA adopt Mexican law?
Bad analogy. The US and Mexico are not connected by an Act of Union.
And actually - parts of Mexican law were incorporated by states in the Southwest, where they made sense: primarily land-use and water rights.
It's a different country with different legal systems.
Act of Union - as I read it - united Scotland and England into the same Kingdom. You guys shared a flag, your armies are the same, the currency is the same.
A difference with no distinction.
Now, a prickly Scot could want to keep his oddball legal system and more power to him. But don't get all irate if the rest of the world looks at that choice and wonders that two countries that share currency, an army, a monarch, and etc should not also share the same legal system.
A better example is the US and Louisiana. While obviously, Louisiana is a state of the union, its laws are based on civil law rather than the common law that the rest of US is based on [1]. It's a real pain when dealing with Louisiana contracts and business.
Another distinction is that Scotland has its own devolved parliament. Some issues, including copyright, are reserved to the UK government, but Scotland can (and does) pass its own laws on devolved issues.
It's a bit of a political minefield to start saying "X isn't a real country". It's easy to come up with subjective rules about why X and Y are the same country but A and B aren't. E.g. is Australia a different country from UK (same queen, based on english law, queens appointee can dissolve parliament, etc.)? Is USA and UK same country (same language, legal system similar (but diverged earlier), similar measuring system (inches and miles!), militaristically have been working together). Is UK and France same country? Both in EU, different currency, but EU law taking precendence? Is France and Germany same country? Same currency, similar (civil) legal system, EU law.
These rules about what makes a country are mostly arbitrary and are often made for political reasons to either give power or take power from certain people.
Bad analogy. The US and Mexico are not connected by an Act of Union.
And actually - parts of Mexican law were incorporated by states in the Southwest, where they made sense: primarily land-use and water rights.
It's a different country with different legal systems.
Act of Union - as I read it - united Scotland and England into the same Kingdom. You guys shared a flag, your armies are the same, the currency is the same.
A difference with no distinction.
Now, a prickly Scot could want to keep his oddball legal system and more power to him. But don't get all irate if the rest of the world looks at that choice and wonders that two countries that share currency, an army, a monarch, and etc should not also share the same legal system.