To answer this question you need to look much further back in time to the Acts of Union 1707. This was comprised of two acts, the Unity with England Act,1706, and the Unity with Scotland Act, 1706. This was the union that created an overarching ‘Great Britain’ and its creation is couched in controversy around how it came to exist. Some believe that post a disastrous attempt by Scotland to create a trading empire left them weakened, whereas others believe several corrupt Scottish Lords were bribed to accept the union. Regardless, when entering negotiations the Scottish were aware that Wales had been absorbed almost entirely by England and so conditions were negotiated by the Scottish. Therefore Article 19 of the Union allowed Scotland to keep its separate legal system. This explains why they were not bound to adjust the law in line with England.
You can read more about the act and all the situations around it here:
or a guardian article on the potential reason for the union here https://www.theguardian.com/politics/2007/feb/08/scotland.britishidentity
or you can read :
Acts of Union and Disunion – Linda Colley
A History of the Scottish People – T. C Smout
For the second part of your question you will need to consider the Wolfenden Report. 1954 which was an investigation, led by Sir John Wolfenden, into the potential to legalise homosexuality and prostitution in the UK. One of the Scottish representatives on this panel was James Adair, an extremely conservative man. Although the Wolfenden report eventually recommended that homosexuality should be decriminalised, Adair stood against the rest of the 14 on the panel and voted not to endorse it. Despite the report being completed in 1954, the conservative people of England still dragged their feet to change the law, eventually doing so in the Sexual Offences Act 1967. James Adair as an elder of the church of Scotland had no desire to allow Scotland to follow suit and he feared that decriminalising homosexuality would destroy the morals of the Scottish. As such he was well reported on for his campaigning against any move forward on LGBT+ rights. He felt that silence across Scotland on the issue was the only way forward. After his removal from the public eye, the tide began to turn and Scotland moved to step in line with England and Wales on the issue, becoming considerably more liberal for the next steps made over age of consent and marriage.
You can read more on this in Wolfendens witnesses – Brian Lewis
Or at : https://www.bbc.co.uk/news/uk-scotland-40731733
This is my first attempt at answering an Ask Historians question so hopefully I have sourced this all ok.