There are very strong lobbying groups that push for accessibility in terms of captions (as well as the “DV” described video audio track) but my impression is that their focus is on the quantity of content that’s covered, and the quality (spelling, time-alignment), and I guess they don’t care as much about text styling.
The requirements are quite high in Canada[1] and have been expanding in the US as well[2].
The company I work for makes products for broadcast customers, around asset management, linear playout automation, and the playout servers that insert the captions (from files or live data sources) so working out how that all happens is part of every big project.
[1] https://crtc.gc.ca/eng/info_sht/b321.htm [2] https://www.fcc.gov/consumers/guides/closed-captioning-telev...
* in terms of 708-only features, not on the pedantic "ATSC uses the 708 system"