'sloppy' originates from English, formed from the noun 'slop' (ultimately from Middle Dutch 'slop') plus the adjective-forming suffix '-y', where 'slop' referred to a loose garment or liquid refuse.

'sloppy' developed in Early Modern English as 'slop' + '-y' to describe things like loose clothing or things like slop, and by later usage the sense broadened to describse untidiness and carelessness, yielding modern 'sloppy' and its comparative 'sloppier'.

Initially it referred to being like 'slop' (e.g., loose or covered with liquid/garbage) or to loose garments; over time it shifted to the current meaning of 'untidy, careless, or of poor quality' and thus 'sloppier' = 'more untidy/careless'.