Ironically this appears to be because another company wanted to protect its trademark.

> In the United States, Tefal is marketed as T-fal. This is to comply with DuPont's objection that the name "Tefal" was too close to DuPont's trademark "Teflon". The T-fal brand is also used in Canada and Japan.

The alphabet T is pronounced "teh" in French. So insofar as the French company is concerned, T-fal sounds close enough to Tefal.

It sounds more like "tay" (as pronounced in English).

https://forvo.com/word/t/#fr

And it would hardly make sense to make a name for US market based on how it sounds in French.