Site full only at weekends

I have just tried to book Bladen Chains for an eleven day stay in July.  Unfortunately my plans have been halted because there is no availability over the weekends in question.

I suppose my point here is this.  Should sites keep pitches open for those wanting longer stays and deprive weekend warriors from there quick stay.

Apart from making it difficult to get a proper holiday in one place of choice the club / site loses revenue  because the days around the weekend are left empty when a longer stay would fill the space.

Thoughts?