I really think "competitiveness" is the last reason, because when the PL took off financially domestically and internationally in the late 90s and early 00s it was not particularly competitive. I mean between 1997/98 and 2003/04 the champions was always either Arsenal or United. And with one exception where United finished 3rd, runners-up was always Arsenal or United. Then Chelsea entered the mix. In the mid- to late-00s , the "big 4" was a thing because the top spots were occupied by always the same four teams and the winner was either Chelsea or United. This "competitive" thing is a bit of a myth.
I think
@giorno has it right that the success is more a result of better commercialization. The Premier League was quicker to target emerging markets, benefitted from a
lower language barrier and higher cultural familiarity (party as a result of colonialization in the past). They had better stadiums (given that they hosted the European Championships in 1996) and a great atmosphere, which obviously made for better viewing. For more casual fans the more "action-packed" style during that period may also have had appeal. In contrast, for example, the Italian clubs were much slower to address markets in Asia, have a language barrier, there is lesser cultural familiarity, no colonial ties and stadiums were crap. Roma, who were pretty much the second best club in Italy in the mid-to-late 00s following Calciopoli did not even have an English language website until 7 years or so ago, I think.
The recent competitiveness of the PL is more result that cause of the financial might of the PL as it is the attractiveness and global appeal of the PL that makes it attractive for all these magnates and other investors. And, of course, that leads to a virtuous cycle. It will be very difficult for other leagues to compensate for that.