' If it was purely about making drivers safer, it would be included in the test.
To be fair probably 90% of drivers will never tow a trailer in their lives.
Being pedantic it's not about making drivers safer it's making drivers towing trailers safer and there is a difference.
Everyone who took a test after that date should have know the rules and if you entered into a job that required you to use a trailer then it wouldn't have been a surprise that you couldn't do without a test.
If it's a requirement for a job then your employer should pay for it just like they would for a forklift test or other safety certificate. If it's for your own business then it's probably tax deductable.
Sadly it's just another thing in life that doesn't suit everyone.