I know little about bpython. I have observed that IPython has very good outreach. Fernando Pérez has promoted IPython at many conferences, helped a lot of people, been responsive to requests, active in the Python community, and all of the other factors that help make a successful project.
It's also been around longer than bpython. IPython started in 2001 while bpython is from 2009.
The current IPython has several GUI interfaces, including through a web browser, with the goal of supporting a graphical notebook with embedded plots and other images. bpython does not support that.
There are very few tools in the extended REPL space. I think software developers don't spend as much time on the interactive shell as computational scientists, and those developers that do may augment the shell with, say, the emacs shell rather than develop a new interactive interface. So an early tool which works reasonably well, which has been around for a while, with few competitors, and has outreach and updates based on user needs, will tend to be more widely used.
It's also been around longer than bpython. IPython started in 2001 while bpython is from 2009.
The current IPython has several GUI interfaces, including through a web browser, with the goal of supporting a graphical notebook with embedded plots and other images. bpython does not support that.
There are very few tools in the extended REPL space. I think software developers don't spend as much time on the interactive shell as computational scientists, and those developers that do may augment the shell with, say, the emacs shell rather than develop a new interactive interface. So an early tool which works reasonably well, which has been around for a while, with few competitors, and has outreach and updates based on user needs, will tend to be more widely used.