For a broader connotation of "slop", it signifies a lack of quality. This is often due to the afformentioned cheapness of food and drink, but often, it is also the opposite case, by means of convenience. Marx gives an interesting comment on the priority of cheapening luxury:
<The price of food has almost continuously risen, while the price of manufactured and luxury goods has almost continuously fallen […] In our age, the superfluous is easier to produce than the necessary.https://www.marxists.org/archive/marx/works/1847/poverty-philosophy/ch01b.htmIn this case, "slop" would refer to fast food, sugary drinks, and so on; i.e. complex consumables which lack nutrition. As we see, poor people are more likely to be fat than wealthy people – this is because of slop, the same way a pig is fattened for the sake of butchering. The cause of obesity is largely determined by excess carbohydrates, and laziness. Carbohydrates are contained in grains, and bread has been the basis of civilisation since early agriculture. The Plebeians eat their bread and have their circus, as remarked by the Roman patricians:
<bread and circuseshttps://en.wikipedia.org/wiki/Bread_and_circusesJouvenal himself sees that the sloppification of culture must itself begin by a decline in the elites, however, which is perhaps corrollary to the convenience of luxury, over necessity, as Marx identifies. Slop is not mere necessity therefore, but is still the lowest order of nutrition. It is not reading books, it is watching television. It is not eating out of cans, it is eating fast food, etc. So, slop has these hidden aspects. The more things change, the more they stay the same. This is anacyclosis.