The content that performs is not the content that recruits
Impressive training footage engages people who already train, which is not who a gym needs to reach.
Heavy lifts, advanced movements and highly conditioned bodies do well because the fitness audience on these platforms is large and interested. Most of them already belong to a gym.
The people a gym actually needs are not in that audience, and when they encounter that content it confirms their suspicion that they would not belong.
Content aimed at them looks different and performs worse by conventional measures. A beginner class, an explanation of how to use something intimidating, the gym at a quiet hour.
That is worth accepting deliberately, because engagement is not the objective. A post reaching four hundred people, twelve of whom are considering starting, beats one reaching four thousand who already train elsewhere.
The practical approach is usually to run both consciously rather than to abandon the first. Community content keeps existing members engaged, and beginner-facing content does the recruiting.