Youre misunderstanding biology’s decision to not impose cognitive assumptions where they cant be proven for a lack of cognition at all.
Bees, a close (relatively) relative of the ant are known to not only play, but also attempt to sneakily reproduce and hide their offspring among the queens eggs. The colony, in turn, murders any bees caught doing so. Clearly more than the simple robotic instinct you wish to imply, and entirely possible for ants to also be capable of. Its just yet to be observed, recorded, and published.
Do not mistake an inability to test and confirm for a lack of capacity.