How do you make more ladies go for 3-3's? Simple - give much more points for triples than for doubles and make it easy to get triples ratified.
Well, obviously triples should be worth more points than doubles, all else being equal. Where there's room for disagreement is at what point underrotated triples should not count as triples at all, and how many extra points good jumps should earn for good quality (+GOE) or lose for bad quality while still meeting the definition of the jump (-GOE).
At the beginning of IJS, skaters lost a
lot of points for underrotated jumps -- anything over 90 degrees short of rotation, and the attempted triple was called as a double, or later called as a downgraded triple.
Under 2005 or even 2010 rules, Sarah Hughes would have gotten no more credit for some of her 2002 triples than she would have for a double. By 2016 rules, some of those would at least be worth 70% of a triple (or 50% for the lutz if called as 3Lze<).
It wasn't until 2010-11 IIRC that the distinction between 90-180 degrees underrotated < symbol and 70% base value was introduced as opposed to the full downgrade << for over 180 degrees short with base value of a full revolution fewer.
So within the past 5 years only it is possible to get some credit for a triple that's not quite around, but up to 180 degrees short. There is still a loss of base value compared to a fully rotated triple, and expected loss of GOE (although in the past 2 years it's no longer required for the final GOE to be negative).
The other rule that has encouraged ladies to work on their triple-triples, and that also has increased the popularity of 2A+3T combinations, is the limit that ladies only get 7 jumping passes in their free skates, and they must include some kind of axel jump.
As of 2002, it was pretty common for ladies to plan 7 triples and a double axel in 8 jumping passes, with no jumping pass more difficult than 3Lz+2T. Under IJS rules, that isn't legal. So for a while at the beginning of IJS 7-triple programs became less common, until more skaters mastered the ability to combine two difficult jumps in the same jump pass. The rule change that allowed full credit for two difficult jumps connected by a half loop, instead of discounting their base value to 80% by calling it a sequence, also helped.