Please could someone help me understand the logic behind 'first time' or 'inexperienced' drivers when it comes to insurance

I have been on a motorcycle for 5 years - as a young male in London, I've had to bear the brunt of various preconceptions around speeding young male drivers and the issue of bike theft in the city. It is also widely known that motorcycle driving is dangerous and requires a fair degree more concentration and experience compared to those who drive four wheels. This year my comprehensive motorcycle insurance came in at £700 - I started at £1900

I recently passed my car test and was quoted £2800 for comprehensive insurance on a Nissan Qashqai (an albeit non sporty, inexpensive 2nd hand). The insurance companies seem to completely disregard motorcycle driving as 'experience' and I am considered a 'new driver'.

My younger sister (age 23) who has been in the car for 5 years, drives a 10k valued car and pays £400 comprehensive
I (age 28) have been on a motorcycle for 5 years, drive a 7k valued car and quoted £2800

Who really has the most road experience? Why is my motorcycle experience not a factor in my car insurance?

Any insight into this topic would be much appreciated!!