Any company will employ a person on the minimum they can get away with.
I got a big promotion on secondment. They refused to pay me more than the very top of my contracted pay bracket (12k less than the bottom of the bracket for the new job!).
I did it for a year and a permanent job in the new department opened up and was advertised at the normal rate for that job.
I applied. I got it. I then had a hell of a fight on my hands to get them to pay me the advertised rate. Their argument was that I’d been happy to do it for the lower rate for a year, why should they pay more.
My argument was that I was doing a job of a senior colleague and that everyone else doing the role at the level I was, was earning about 50% more than me. That they were giving me more and more responsibility over people who had worked there years and were paid better than me. In the end, what clinched it was when I told them that I’d decline the job offer and go back to my old job for an easier life if they didn’t pay me appropriately for the harder job!
And telling my new line manager, who hadn’t known about the pay arrangement for my secondment and told me that he was embarrassed for them that they expected me to work for so much less than everyone else.
Was it because I’m female? Maybe, maybe not.