Perl 5 also had OOP, but neither Perl nor Tcl could credibly claim "native" OOP during the relevant time frames. By contrast, one of Python's founding design goals was OOP.

Ruby didn't have very much mindshare in the U.S. during the relevant period. Which is a real shame. There's always been a significant amount of great work coming out of Japan that never gets popular attention elsewhere. Ruby is one of the notable exceptions, though it's break-out success came belatedly. (Wikipedia says the first English language Ruby mailing-list was created in 1999. AFAICT, O'Reilly's first Ruby book was "Ruby on Rails", published 2006. O'Reilly's "The Ruby Programming Language" wasn't published until 2008. All of these are indicative of an exceptionally late popular introduction to the English language programming community.)

I don't mean to imply that luck had nothing to do with Python's success. It's just that if you look at the contenders at the time and the qualities that people were (rightly or wrongly) looking for in a programming language, it's not at all surprising why Python gained popularity. To the degree luck had anything to do with it, it was largely the timing of those nexus of factors.