But it didn't and it isn't. Debian created DEB three years before RPM was created. Starting out, RPM didn't even support dependencies. I got into Linux before RPM so Debian was the obvious choice. I never understood why RPM was created.
The reason I chose debian in the first place was because of the superiority of apt-get and debian/rules over getting random things from rpmfind.net
I thought redhat distros later introduced yum as the "apt" equivalent?
This is up to the repository. If Debian choose RPM it would be as large as it already is