The point of multiple seating and pricing tiers is to capture as much of the consumer surplus as possible. Different people are willing to consume the same product at various prices, thus cheap seats and expensive seats exist to segment and capture as many different points on the soccer game demand curve as possible. In effect turning one large supply demand chart into multiple smaller ones via subltle alteration of the underlying good.
Doing what you suggest goes against that rather basic economic principle.
Though as
Ulrich suggests, there might be much more lightly attended teams that do this anyway, some English teams in league 1 only draw 2000-3000 people I believe they are broadly general admission.
