What you train is what you get. Few of the U.S. pair teams do singles training in addition to pair training. When my daughter trained pairs in Colorado Springs, she was one of the only skaters who did a 45-min singles session and lesson with a singles coach every day. Most of the pair skaters did pair sessions only, focusing on pair elements and programs. In fact, very few of the pair skaters there had passed a senior singles freeskate test, partly because they don't skate singles anymore and partly because they don't see any value in doing so. If a skater does not begin skating pairs with a mastery of all double jumps and preferably a few triples, it is unlikely that the skater will develop them while doing pair skating. I'm not sure how skaters in other countries develop their triples, but they must be doing singles training in addition to their pair training.