It's because of the brutal reality of racing.

It's because owners and trainers don't believe she's physically ready to be on the back of their horse, in a brutal two-mile race, in a field of 24, worth $6.2 million in prizemoney.

It's because in May she fell during a race at Mildura, a horse stomping on her abdomen, her pancreas split in two, and doubts remain about how much she has recovered.

And, to be frank, it's because of other reasons, too. Reasons that everybody whispers around the track but won't say publicly.

It's because, after winning the Melbourne Cup last year on Prince of Penzance at 100 to 1, she immediately went on the front foot and blowtorched owners and trainers for constantly overlooking female jockeys – the ultimate biting of the hand that feeds you.

It's because the same people also believe that Payne has become caught up in her own hype, read too much of her own press, is too quick to dismiss others through her Twitter account.

And it's also because – and this one is delicate – if you ask enough people in the racing industry they will tell you that Michelle Payne is a good, solid jockey, but she doesn't get the rides of Hugh Bowman and James McDonald and Damien Oliver because she is not in their class.

You're a fool if you think discrimination doesn't exist in racing. But you're an even bigger fool if you think connections wouldn't hesitate putting a garden gnome on the back of their horse if they thought the gnome gave them the best chance to win.

It's for all these reasons that Payne, on Derby Day on Saturday, almost a year after she busted down the door with victory in the Melbourne Cup, will have just one ride at Flemington.

She will saddle up the filly she also trains, Queen Of Zealand, in the Wakeful Stakes (2000m).

It's a solemn reminder of how harsh the racing industry can be. Where outsiders will say it's because of her gender, those inside the tent understand that winning a Melbourne Cup does not entitle anybody to a ride the following year.

Payne is racing's great conundrum right now. She should be the face of this carnival, indeed the sport.

After her win last year, Australian Turf Club officials in Sydney rushed her to Randwick for a meeting and she was swamped by racegoers and autograph hunters.

What isn't commonly known is that the club desperately tried to secure her rides with several trainers. Some assurances were made but she was unwanted.

Her victory on Prince of Penzance saved the Melbourne Cup: a victory for a laconic trainer, with a cheap local horse, leaving expensive types from Japan, Ireland, Germany and all of Europe in their wake.

But much of that was lost when Payne bravely used the victory as a platform to lay down the law for female hoops, on Australasian racing's grandest stage.

"I feel like a lot of the time I get taken off horses because they say, 'she was unlucky' or 'she missed the start' or 'she couldn't get out'," she said. "Then the guys get on the horse and do the same thing. And they say he was unlucky and he couldn't get out. That drives me crazy. A lot of the time I'm more dedicated than a lot of those guys are and I get less opportunities. You try so hard in each race. It's just frustrating. I don't know if it helps – but I hope it does."

You go, girl. Or something like that.

When she won the race, I was standing in the mounting yard next to Kim Broadfoot, whose husband Andrew was a part-owner of Prince of Penzance.

"She's such an inspiration for these girls," said Kim, wiping away tears, pointing to her three young daughters getting crushed in the mounting yard madness. "She's been a great, positive example to my kids. It's such a male-dominated sport. It's an inspiration because she's such a strong woman."

Since then, though, she has been at war with the industry.

When the owners of Prince of Penzance told her she would not be riding the horse when it resumed in the Memsie Stakes, she angrily tweeted: "Not anymore I'm done, why work your arse off for people who don't appreciate what you do and write you off anyway #moretolife".

Owners can put whoever they want on the back of their horse. It's the privilege that comes with paying the bills. Payne is not the first jockey to lose the ride on a horse. Again, the harsh reality of racing.

Her bitter dispute with Racing NSW officials earlier this month was comical.

Payne – and others – painted herself as the victim when she was told she could not ride in NSW because of a law introduced earlier this year forbidding those with trainer-jockey licences to race.

In Victoria and other parts of Australia, you can. NSW banned the practice for integrity reasons, wanting to keep a clear line between trainer and jockey.

It was introduced to protect the reputation of racing – not to upset Michelle Payne.

Doubtless, some will consider these words to be an attack on a female jockey.

When I spoke to several jockeys, trainers, owners, officials and racing experts about this column, they all said to drop off and find something else to write about.

A simple analysis of Payne's career as it stands, though, has nothing to do with the fact she is a woman.

It's because she's a jockey.