Does the Cavalier fighter’s usage limit on the Unwavering Mark feature apply to the creatures you can mark, or just the bonus attacks you can make?

Does the Cavalier fighter’s usage limit on the Unwavering Mark feature apply to the creatures you can mark or just the bonus attacks you can make?

Basically I’m curious if just the attacks are limited or if it is the mark itself that is limited. If it is the mark itself that is limited then the power disappears pretty quick and is not super useful, but if it’s only the attacks that are limited then the marking can be useful for a long time and should be used on multiple enemies every turn if possible, to avoid having others take damage.