Fun fact: The X-Files production team foresaw the coming of 16:9 home entertainment, so they made some effort (increasing with later seasons) to try and "protect" a 16:9 frame, which allowed for an unusually good 16:9 Blu-ray restoration. [https://www.tweaktown.com/reviews/7499/look-inside-the-files...]
I learned this from the older X-files DVDs, which have some unusually good special features.
I saw a movie in a theater years ago where the projectionist did not change the lens and/or mattes when switching from previews to the main feature. The projected image was much taller like a 1.85 or a 1.78, but the feature was shot wider 2.35/2.40. However, the image wasn't protected for the taller aspect, so all of the on set gak could be seen as it was never meant to be shown at the taller aspect ratio.
I've also sat in transfer sessions where the Pan&Scan decisions were being made to transfer wide screen down to 4:3 vs just doing a center crop extract. It makes you appreciate just how much effort is needed when done as best it could be rather than just the fast/lazy way.
Not saying it had anything to do with X-files, but also when you shot something for TV but were not entirely sure if the capture would ever go to the movies, you protected the wide frame.
Also, if you shot a movie but wanted it to look good in TV later, you put the most important action somewhere in a 4:3.
I never watched the widescreen version of The Wire they put out years ago but now I'm curious again. That show was a bone deep 4:3 product and the show plays with it constantly. Here is an interesting breakdown that made me really appreciate how clever they got while trying to be pretty subdued with the cinematography on The Wire https://vimeo.com/39768998
Similar with Babylon 5, although the CG has not aged as well.
Not to dismiss the X-files team, but 16:9 was already around when they started. Just not in the states. Japan started getting 16:9 CRTs in the early 90s, Europe followed in the mid 90s. America lagged another half decade and effectively skipped 16:9 CRTs mostly going straight to plasma/lcd.
Although Stargate SG-1 (1997) was filmed in 16:9 from the outset, earlier seasons were broadcast in 4:3.
The first season or two you can definitely see the crew in the safety margins, sometimes the camera crane too
When you have an OLED screen then 4:3 aspect ratio is fine because the black bars aren't backlit, so it's not a problem.
The article mentions that Mad Men was already in 16:9 so the issues are unrelated to re-framing.