The cataphract's weapons included:
- Composite bow: Same as that carried by the Toxotai.
- Kontarion: or lance, slightly shorter and less thick than that used by the skutatoi which could also be thrown like a pilum.
- Spathion: Also identical to the infantry weapon.
- Dagger: Sometimes referred to as a "Machaira"
- Battle axe: Usually strapped to the saddle as a backup weapon and tool.
- ofc arrows for bow
en.wikipedia.org
That is just one example for historical reason but also gameplay what I´ ll try to describe:
Right now most melee mounted troops are geared quite purely, especially if they are dismounted their lances are useless, Even worse case are "medium" cavalry having short spear not good from horseback, one bag of not efficient javelins (besides jarids) and useless short melee weapon good only when dismounted.
If ai could fight with spears more like RL not what we have perhaps those slots would not be that missing, same for most throwing weapons. But spear fighting was broken in warband too so I do not expect to have it good in BL especially while all that beta time did nothing to make spear units usefull besides occasionally countering cavalry.