Another question that can be answered by some Google graphs.
According to Google Ngrams, for Lisp (whole family) in late 1980's;
for Scheme alone quite a bit later.
I'm surprised that the loss of the popularity is so great.
if you like this post, you might be interested in following posts:
Why you do not use Lisp? The results of the poll.
Relative popularity of Lisp dialects.