Post Request is not returning same object as passed - asp.net-mvc

Question

I am trying to do a simple CRUD app asp.net core using MVC and the strangest thing is happening to me.
create the model and pass it in to the form but when I go to save it, it no longer has the Id that I passed into it.
[HttpGet]
public IActionResult CreateCompany(Guid id)
{
//id = 677b57f1-d0b2-484b-9892-b06e6eb9f1f7
var pageId = id;
var company = new CompanyListItem() {PublicPageId = pageId};
return View(company);
}
[HttpPost]
public IActionResult CreateCompany(CompanyListItem model)
{
//model.PublicPageId = 00000000-0000-0000-0000-000000000000
if (ModelState.IsValid)
{
model.Id = Guid.NewGuid();
var newModel = _companyDataProvider.Add(model);
PublicPageViewModel page = null;
if (newModel != null)
{
page = _pageDataProvider.GetPageIdFromCompanyListId(newModel.Id);
}
if (page != null)
{
return RedirectToAction("Details", page);
}
}
return View();
}
my form:
#model CompanyListItem
<h1>Add Company</h1>
<form method="post">
<div class="col-md-6">
<div class="form-group">
<label asp-for="Header"></label>
<input asp-for="Header" class="form-control"/>
</div>
<div>
<input type="submit" class="btn btn-success" value="save"/>
<a class="btn btn-default">Cancel</a>
</div>
</div>
</form>
Does anyone know why this is happening? Or how i can prevent it from happening?