That's because FT had the government as their shareholder and they were trying to protect their investment. That's definitely another important factor but the fact that minitel actually worked was definitely a detriment.
I remember visiting France during the Internet boom in the rest of Europe and people there were proudly showing off their minitel terminals (tiny little screens with a slide-out keyboard) and what they could do with it and how they didn't need this newfangled American nonsense in their houses.
Of course that didn't hold in the longer term but it certainly did not help early adoption.
I remember in 2002, when my family, and all my friends' families had an unlimited internet connection, having to use the minitel to register to some exams for some Universities. It felt like an anachronism. So unconvenient. I wouldn't be surprised if the government played its part in leaving it that way.
The next year though, they changed it and we could register through internet.