If a multishipper says they like Cedric/Harry, you can tell where their favouritism is directed at based on their opinion on Tom/Harry.
If they don't like Tom/Harry then congrats, they probably like Cedric/Harry way better than any other pairing they ship.
If they like Tom/Harry then it's clear they favor that pairing more than Cedric/Harry.
I've never seen anyone who likes Cedric/Harry more than they like Tom/Harry which is disappointing.
People ship Tom/Harry simply because Harry described him with attractive features. Oh, that and because people like to insert themselves as Harry while feminizing him to no end. Tom killed Harry's parents and took his childhood in the process whether you like it or not.
Cedric was described by Harry as attractive too but unlike Tom, they actually had tension and potential chemistry because they casually interacted in canon.
But alas, people like shipping Harry with Tom more because they like the dark thrill of it. Cedric is a way better option to keep Harry in character while also making him romantically interested in a tall and attractive brunette.