It's possibly the same at grounds all over the country but my own personal experience [at city] of what has affected the atmosphere over lets say, the past 10 years or so, has been the commercialisation of football culture. The modern football fan is a commodity and as such can be molded into what our [I say our owners but I really mean the people who are trying to control football culture], think makes us more like consumers.
Trying to keep this as brief as I can, as consumers we create profit. As a commodity we can be controlled. As supporters we create atmosphere; in order to create atmosphere we need to be free, we can't be controlled. A good example of this is the spontaneous outburst of bluemoom at the start of a match vs the false, fake, created bluemoon that is bellowed out to us instead: they own the atmosphere because they own us, we're the commodity, and as such should be controlled and molded.
They will use football violence as a reason for this control. But I think it's an excuse to medicate us all because a few of us have what is often referred to as the English Disease. The matchday experience is no longer one where we can be free to express and indulge in what I would call terrace culture (and what others would ask to define in order to be pedantic purely for the sake of taking a counter argument). Instead we're supposed to be consumers.
The consumer, the molded commodity, is controlled. It is a part of the atmosphere that's created for it and it does as it's told. The supporter, when deviating from this ideal model, when creating its own atmosphere, becomes something that needs to be eradicated or subdued. We need to play our part in the created atmosphere or risk being secluded from it.
How do they eradicate us (terrace culture)? They ban us, have stewards tell us to sit down, be quiet, ban drinking in grounds, police us....etc, etc.... often under the guise of anti hooliganism. Which would be fair enough if that's all it were. But who defines hooliganism? And what if purely participating in a past tradition of being a supporter meant your behaviour was classed as hooliganism? Then, anything that didn't fit the mold of the desired consumer could be classed as anti social, criminal, hooligan.
And you would be banned.
So you do as you're told. And you consume. And the atmosphere you once created is now something you observe as an outsider.