Why do airports have directional runways instead of a large area to operate in any direction?
The typical World War II "A" runway shape solves this issue, without covering a huge amount of area with concrete, etc. Even so, that configuration has fallen out of use in modern airports. 

Ultimately, this is a solution to a problem that doesn't really exist and a problem which has a more efficient solution that was already widely used.

With respect to your particular question - to some degree, this is exactly how original grass fields were treated. But no matter how convenient, there's always a need for consistency and predictability and you can see how that has developed to what we have now. Taxiing a heavy airliner isn't a trivial task - doing so with no markings or defined route sounds terrifying.

Additional practical issues of your large slab of concrete vs. a defined runway:


No ILS
No runway lighting
No runway markings
No threshold, no touchdown markers
Far more difficult to precisely define runway length
Very very difficult to accurately describe a particular location and route


To be honest, the list goes on and on and I'd struggle to imagine commercial ops being able to operate like this safely and efficiently.