Most Latin American countries had weak or non-existent public service television, so there was no real incentive to introduce teletext technology, regardless of whether they used PAL, PAL-M, or NTSC. There were (and are) few BBC- or even ITV-style broadcasters in Latin America. For the most part, they are privately owned, fully commercial, and with few public service obligations.
I'm not confident that this was the reason. I think the basic summary of what happened in the countries that used NTSC was that commercial broadcasters had to work with whatever TVs were used in the country and they didn't have teletext decoders installed. If a situation had emerged where over half of all TVs sold in the late 1980s had teletext decoders then it's possible that some broadcasters would have tried out teletext services in one form or another as the receiving infrastructure is already in place.
Brazil is an oddity when it comes to TV standards and is also a country with a large population. Does anybody know anything about the PAL-M TVs used in Brazil, such as which companies manufactured them or whether they are unique designs or modified NTSC TVs etc?
The cost to a TV company of implementing a (basic) teletext service is quite low. It doesn't necessarily have to be anything as grand as Ceefax or Oracle.