The switch occurred while I was at Berkeley and it also made me sad. I loved that course so much I decided to TA for the self-paced version which kept SICP and Scheme.

Brian Harvey explained the decision to switch here:

"But, as I keep saying, the choice of programming language isn't the main point. I get upset when students, even the students who like 61A, refer to it as "the Scheme course." It's not a course about Scheme! It's a course about programming paradigms. MIT, where SICP was written, no longer includes that course in its lower division core sequence, not because they wanted to change programming languages, but because they changed the entire sequence from courses organized around big groups of ideas to courses organized around application areas: first "let's build and program a robot" and then "let's build and program a cell phone." That's a brave and thoroughgoing attempt to, among other things, attract non-nerds to computer science. To say, as some people do here, "MIT switched from Scheme to Python" completely misses the point of what MIT did; nobody is proposing any change half as profound at Berkeley." [1]

[1] https://people.eecs.berkeley.edu/~bh/61a.html