Photos rejected

> still can't get my head around why other platforms accept the same image?

Perhaps when Adobe entered the market they decided to do things differently (for their commercial benefit), providing a higher baseline standard. 

> It should in my opinion be up to the buyer's to decide what they wish to purchase

Many faults are not visible in proof images. I see first hand what happens if a poor image makes it into Adobe's library; the customer buys it, they complain and ADOBE'S REPUTATION SUFFERS. This matters to Adobe's business model. 

In any case, Adobe are under no obligation to be fair to contributors. Your relationship with Stock is not as a customer it is as a supplier. The life of a supplier of any product to any business is hard and competitive, and the behaviour of companies to suppliers is often capricious and challenging. Suppliers have the choice of competing and adapting, or not being a supplier. If of course Adobe annoy their suppliers too much and the supply suffers, then they will need to change, but right now the tens millions of photos seem to show otherwise. And the people they annoy the least in this way are established commercial photographers who have the same view of quality that they do.