I would guess the order just indicates they started as a fighter, not that they are mainly a fighter. So a 1 level dip into fighter first for heavy armor and a fighting style, then melee warlock from there makes sense to me.
Otherwise, maybe it's just people thinking that fighter 5/warlock 5 gets you just as many attacks as a full fighter, and also fireballs/hex etc
Right now the Pact of the Blade Extra Attack stacks with the Extra Attack gained from Class features and going Eldritch Knight gives access to the Shield spell and some lower lvl spell slots.
Warlock 5/Fighter 5/Paladin 2 and Warlock 5/Paladin 5/Fighter 2 both hit extremely hard. Only Paladin 2/Swords Bard 10 really out performs them for melee burst damage.