[Tempora]

Saban/Disney paid for the international publishing rights (anywhere outside
of Japan) to Toei's Super Sentai TV
series. With these rights, they could distribute it any way they want,
either subbed/English dubbed (e.g. Ultraman Tiga,
the English dubbed Abaranger epsiode in that one episode of Power Rangers
Dino Thunder),
or adapt the show (e.g. Power Rangers, Super Human Samurai Syber Squad).
As we all know, Saban/Disney chose the latter.

As an aside, even Hong Kong television, which shows a lot Japanese shows,
end up showing Power Rangers, not Super Sentai,
because even though it would've been easier for HK to get the Super Sentai
show from Toei,
Saban/Disney holds the rights to these shows outside of Japan, so what
Saban/Disney offer is what they
get, and what they offer is Power Rangers.