It would enable afk farming of relics, which would in turn incentivize botting. Botting in F2P games is a constant battle, and taking steps to prevent it is not imprudent.
However, it's an overstep when anti-afk measures have a noticeable impact on legitimate players. This is currently the case with reactant, particularly when the mission type is very fast-paced, like void cascade or capture.
Low spawn rate is also a contributing factor, which is why the meta for interception fissures is to hold 3/4 objectives until everyone has a relic unlock. Or, more accurately, it's why nobody runs interception fissures.