I think the issue is the difference between combos ending in a loop and those ending in a toe loop.
In Alina Zagitova’s case, she does the 3Lz-3Lo, or triple Lutz-triple loop. In order to take off for the loop, the skater has to keep their free leg in front of their body after landing the first jump (rather than swinging it through on the landing), and quickly pull in to take off for the loop after landing the first jump. The Lutz lands on the back outside edge, which is the takeoff edge for the loop. In order to make the combination work, the skater has to do the loop almost immediately after landing the first jump in the combo, as they won’t be able to generate the force for the jump if there’s a delay.
The toe loop is a toe jump, that is, the toe pick is used when taking off for the jump. Unlike the loop, the toe loop doesn’t have strict timing requirements, so after landing the first jump in a combo, a skater can delay slightly to adjust for a bad landing, then touch the ice with the toe pick and add a toe loop for the combination.
tl;dr physics requires loop combos to be done quite quickly, while toe loop combos have more leniency
One of the positive GOE bullets is “effortless throughout (including rhythm in jump combinations).” A successful loop combo requires good rhythm, as otherwise the combination wouldn’t work. For the toe loop, there shouldn’t be excessive delay between the first jump and the toe loop; after landing the first jump (on a back outside edge, as always), the skater should quickly touch the ice with their toe pick and vault into the toe loop. All jumps in a combo should have “very good height and very good distance” in order to satisfy that positive GOE bullet as well, though some skaters will get more height on the toe loop than the first jump (or, in cases in which the toe loop is tacked on after an iffy landing, the toeloop will be noticeably poorer in quality).
A combination is ruled invalid if there is a transfer of weight from the landing foot to another part of the body (hands, free leg, etc.). All jumps land on a back outside edge, and the toe loop and loop take off from the same edge, which is why they’re the second jump in a combination. If a skater can’t control the landing of the first jump, there are GOE deductions for performing, for example, 2 three-turns between the jumps in combination, loss of rhythm, etc.
In ladies, the 3Lz-3Lo is the most difficult (and highest scoring) combo outside of anything with the 3A (which is not common enough to be anything other than an exception to the rule at this point). 2A-2T-2Lo is also a common three-jump sequence (double Axel, double toe loop, double loop). Fewer men do loop combos, though Adam Rippon is a notable exception.
