Maybe that’s how it originated?
Welcome to the wonderful world of .. "standards, custom and practice, policies, guidelines, and rules" you can stick the lot of them in air quotes. Even when you read the RSSB standards they are listed only as 'guidance' and TOCs can set their own rules. There are a lot of 'standards' that are based on agreements from ATOC. Its like the 225 'rule' Technically its only 'guidance' based on 'agreement' from ATOC.
The 'standards' are there for a reason and TOCs do agree to them and also collectively decide when to change them. It used to be that the tests were set in stone but TOCs have been given the freedom to set higher standards and set additional tests. That additional flexibility is what we see today in the current standards and today's testing.
With the EU license part of the requirements for getting one is that you are trained to a 'standard' and that because you have one it proves that this 'standard' was met. In the TDLCR (Train Drivers Licences and Certificates Regulation) you have a more mandated set of rules that are required; which is the legislative side.
The TOCs are very much part of the machinery that sets all the standards. BUT that means that everyone agrees to adhere to them. The 'standards' are pretty much the 'rules' we live by. There are group standards for pretty much everything :/
Another thing that comes up quite often is the eye test. TOCs use the Ishihara plates to test colourblindness. The TDLCR states "normal colour vision: use of a recognised test, such as Ishihara, as well as another recognised test if required". The Ishihara is cheap, quick, easy and a valid test so the TOCs all use that BUT they
could use a lantern test. The standards allow for some flexibility but the TOCs all gravitated towards the same test. This in some ways, is good. It provides a fair across the board approach and having a standard that everyone meets allows Driver to move anywhere in the country.
Having those 'standards' is integral to what drives the railway. it is the glue that keeps us together and keeps the entire network safe. We can all split hairs as to how they are created but they are followed like commandments but written in blood.