3 ideas
An untrained lifter can add weight to the bar every single workout because their recovery and adaptation cycle completes within 48–72 hours, matching a three-day-per-week schedule. This window closes as the lifter advances, which is why beginners can progress workout-to-workout while intermediates require weekly and advanced lifters monthly cycles to drive the same adaptation.
A barbell movement's correct depth and path are dictated by the anatomy of the joints involved, not by convenience or load — the squat below parallel, the press locked overhead, the deadlift from the floor. Partial movements train only a fraction of the musculature through a fraction of the useful range, making them a different and inferior exercise rather than an easier version of the same one.
Because free-weight barbell movements force the entire body to balance and coordinate the load along a vertical line over the midfoot, they recruit far more muscle mass and stabilizers than machines that isolate movement to a fixed path. This whole-body integration is what produces general strength that transfers to real-world tasks, which machine-based isolation cannot replicate.