First of all, I think your hair's curl pattern still looks really nice!
It is possible that your hair's curl pattern has just changed over time. If I had to guess though, I'd say that your hair may be getting damaged, and therefore straighter, from all that straightening.
So I guess try cutting down on flat ironing as much as possible? Do you have the type of hair that you can blow dry straight? (I do, but my waves are really weak) Otherwise, use the lowest heat setting that you possibly can.
I'm actually more than somewhat disappointed that they require you to straighten your hair.