In my opinion, this is pretty normal. Barbell, dumbbell, and machine workouts/weights are not all equal.
Comparing weight for weight, the easiest level of workout is (1) the machine, (2) the barbell, then (3) the dumbbell. Certain workouts you might swap (2) and (3) but I'm going to focus on the bench press. Here's my reasoning for why:
- Stabilizer Muscles: when doing a barbell press or dumbbell press your body is using more than just the pectorals. A range of "stabilizer muscles" are involved in order to keep balance and proper movement.
- Direction of Movement: On the topic of movement, in the chest press machine the range of motion is limited. There is no drift: all your effort is directed directly to the pulleys in order to pull up that stack of plates. In a barbell bench press, your stabilizer muscles are required to keep the bar from drifting forward or backwards. In a dumbbell bench press, you also have to keep the dumbbells from moving left to right!
- Mechanical Advantage: 100 lb on a chest press machine is not necessarily 100 lb. You've mentioned pulleys, so the first thing to look for is if you have any double pulleys. If you do, the weight is actually half of what you're reading. If you've selected 100 lb but there's a double pulley, it's only 50 lb and your increments are all half weight as well.
- Safety: one thing I think a lot of people forget is that there is an inherent safety with respect to a pulley machine. You can try a harder weight, fail easier, reset quickly, and it is extremely hard to hurt yourself. Compared to a barbell bench press where loading up a challenging weight can cause injury, I find that some individuals are afraid of pushing themselves.
In summary, I think it is completely normal that you're making more progress on weight machines. For reference, at my own gym, I can max out the chest press machine (~300 lb), my barbell bench press max is 230 lb, my dumbbell bench press max is 160 lb.
