Because it is never how it works according the news and press. Spend 3-5 years in any industry doing supply / demand side you will quickly realise the media, despite 10 - 30 years of experience have near zero idea on how any things works.
Manufacturer are happy to lower price, including DRAM and NAND which I get stick for even saying it. As long as you are willing to sign long term agreement with significant volume. This is the *only* way they could ensure they do their capacity planning right, and even planned out additional capacity building. This may also including commitment to certain next gen display panel with minimum price guarantee.
But Apple has always preferred to have flexibility over commitment. That is why they keep themselves agile.
And as I have written before, They don't actuallypay $100 for those panels, there are always different rebate somewhere.