It failed mainly because of the fragmented nature of American TV. They didn't have a duopoly of to broadcasters who could decide and develop a universal system and then roll it out across their channels.
An effort was made by the FCC to come up with a standard, but as I understand it, while the TV manufacturers and most US broadcasters wanted to adopt the BBC/IBA standard, a few -including CBS- felt the French system was far superior.
The CBS lobbied the FCC to make the French Antiope system the standard teletext protocol for the US but later abandoned the system in the mid 1980s in favour of NABTS. Antiope enabled TVs stopped being manufactured in 1987 and Antiope broadcasts ended in France in the early 1990s after France adopted the British teletext standard.
A competing system to both Antiope and the British teletext standard developed in Canada was NABTS (North American Broadcast Teletext Specification) that was adopted by both NBC and CBS but it failed due to the high cost of the separate decoders that were generally only sold in a small number of localities where TV companies operated NABTS services. NBC discontinued NABTS in 1985 and CBS followed a year later. Despite the lack of commercial success of NABTS in the 1980s, decoders were included in analogue TV tuner cards for PCs manufactured in the late 1990s and 2000s.
Following the failures of both Antiope and NABTS in the US, Zenith tried to create a US teletext standard in 1986 by including a teletext decoder module using the (then firmly established in many countries using PAL) British teletext standard in the Digital System 3 sets. A limited number of TV channels made use of these teletext decoders, the most prominent example was the Electra service on the cable channel WTBS, but by then the major national TV companies like NBC and CBS had given up on teletext. Rather strangely, no Japanese TV manufacturers sold any TVs with integrated teletext decoders. This could well have been a major factor why few TV companies decided to operate teletext services.
Competing with teletext for VBI lines was the National Captioning Institute which was established in 1979 several millions dollars of start-up funding from the Federal government and the support of the US Department of Health, Education, and Welfare. The technology behind closed captioning was developed in the US during the 1970s. In 1980 NBC and PBS started including closed captioning to their programmes but CBS decided to offer captioning using Antiope instead. Originally a set-top box (manufactured by Sanyo and sold through the NCI) was required to receive closed captioning as no TVs included a closed captioning decoder as standard. Sanyo determined in the late 1980s that it would be less expensive for the public to buy a TV with an integrated closed captioning decoder rather than a set-top box. The result was that Sanyo lobbied Congress, with the backing of an expert witness testimony, to pass legislation requiring all TVs to be sold with a closed captioning decoder as standard. The Television Decoder Circuitry Act became law in 1990 and gave the FCC powers to enact rules on the implementation of closed captioning decoders in TVs. The FCC mandated that all TVs with a screen size of at least 13 inches manufactured after 1 July 1993 must include a closed captioning decoder as standard.
In 1990, the Americans with Disabilities Act became law and required that TV programmes included subtitles for deaf people although it did not specify that closed captioning should be used rather than teletext.
Zenith decided that it would not be practical to redesign their TVs to have both a teletext decoder and a closed captioning decoder so decided to eliminate the teletext decoder from their 1993 range of TVs. This effectively ended teletext in the US in 1993 and the Electra service also shut down that year.
There are questions whether the disability movements in the US and the US Department of Health, Education, and Welfare were aware of teletext and that it could be used for subtitling programmes (as it was in the UK and Europe) as an alternative to closed captioning. Between 1986 and 1993 both teletext and closed captioning existed in parallel to each other in the US. Did Zenith and teletext service providers ever respond to the lobbying by Sanyo to Congress for closed captioning decoders to be included in TVs as standard, that teletext can also provide subtitling so teletext decoders should be included as standard instead? One could argue that the fragmented nature of American TV and the failure to come up with a teletext standard before 1986 were significant factors hindering the deployment and uptake of teletext services in the US but they were not ultimately responsible for its failure (to even catch on?). Would history have been different if at least one of the major TV networks had decided to offer teletext services nationally after 1986 using the British teletext standard as used with Zenith TVs? Would history have been different if Japanese manufacturers had included integrated teletext decoders on their mid to high end models after 1986 even if initially very few TV companies offered a teletext service? Was teletext ultimately killed off in the US by the disability movements in conjunction with Sanyo who were backing closed captioning instead?