I was born in the USSR but was in New York for Jr Highschool and Highschool. Whenever my dad saw the math curriculum he assumed I was in some sort of "slow program" - he could not believe that the mainstream program is that un-challenging.
I bet there's a lot of factors to why curriculum gets watered down but I do think recent focus on how kids feel about school, self-esteem, safe spaces, etc goes against hard-core curricula.
When you learn for real (and this extends to adults as well) you are confronted with things you don't know how to do, and you have to bang against them for a while to solve them and learn. That feeling of "wait, maybe I can't do this / I don't get it" is a negative one. And it does create a situation where some percentage of kids can't hack it, so they are excluded/left behind.
I think as a culture we've been making the choice to teach/do easy things that everyone can participate in, rather than do challenging things that will force some people to grow more while leaving some behind. It's not a choice I agree with but I guess I can follow the zeitgeist and logic of it for a certain extent. It's the same as NYC, SF and other cities getting rid of the specialized schools with entrance exams. Since some people can't hack it, it's an exclusionary approach and therefore getting rid of the exams on one hand equalizes access on the other hand waters down the standards.
I do think there will be unintended but obvious consequences as we're seeing in this story: parents who know better, who want the best for their kids will invest in tutors, private schools, etc that challenge their kids when the mainstream schools do not. The effect will be that within the school system, everyone is doing easy things that everyone can do, but in outcome space there will be a larger gap between kids of parents who care/can afford something beyond public school and those who cannot. In the long run, this will cause greater inequality because there will be come percentage of kids whose parents can't give them a leg up that would have risen to the challenge in a tougher curriculum but now will not have a chance to do so.
In my eye this is unfortunate both because we're creating a less educated populace and a less confident one. The idea of being brave and confident means you take on a challenge knowing you have a good shot of eventually overcoming it. This holds at school and it holds in the work place. I am not sure how many people who never had their ass kicked (for a while) by school work and then had the experience of "getting it" will then come into a work situation and be able to "stretch" by taking on work they don't quite know how to do yet. Not the path I am chasing for my kid.