Its part of the growing pains of the migration from analog TV to digital, which brought with it an aspect ratio change. And change is never easy.
Things had been mostly quiet lately, because almost all HD commercials and some HD program content as well, were typically what is termed "center-cut safe", which means you can safely take 16:9 material and center-cut it (cut off the info in what would be the pillar regions) so that it then fits in a 4:3 hole, and if no pertinent info is in the pillars, no pertinent info is lost, even though the pillar regions are discarded. If you frame content so that no real action or graphics happen in the pillars, HD video then works in 4:3.
But the entire idea is for 4:3 to go away at some point.
When broadcast stopped sending SD channels in 2009, cable and satellite wanted to maintain a SD feed of those channels, but they were no longer available, so they took the HD feed, down-rezzed it to 480i, and center-cut it to 4:3. That was soon followed by cable and sat networks dropping their SD feeds as well, and the vendors used the same process to maintain feeds of those channels for SD customers.
That was a good solution at the time because most all content was center-cut safe. But lately producers have gotten away from framing for 4:3 (which was the normal method) and are now framing for 16:9. It's annoying on programs watched on a 4:3 feed, but now commercials are starting to be non center-cut safe as well, so content distributors have to either solve that or not get paid. And right there is the motivation which until lately, was missing. Just a year ago virtually all commercials were center-cut safe, but that is ramping down quickly, driving the need for a better solution. And that is why we are seeing this change on some channels already.
There are two basic solutions:
The first is to force the SD version of the HD feed into a letterbox mode, 24/7. That is even more annoying for SD viewers, and when the source is a 4:3 original with wings added for HD 16:9, and you take that and letterbox it, you get a postage stamp. Exceptionally annoying. But at least the commercial graphics don't get truncated this way and broadcasters will get paid, which is the only reason we have a video industry--it getting paid.
The other solution depends on AFD or Active Format Descriptor, which is a 4-byte flag in every packet header that tells the target device what to do with each piece of video on the fly, and how to handle it for a 4:3 target and how to handle it for a 16:9 target at the same time (as well as choices for 14:9, one large bar just at the bottom, etc.).
Using AFD, video can be letterboxed if that is desired (for instance, 16:9 video that is not center-cut safe) on a 4:3 screen, center-cut (if the video is framed for that), or any of 8 other modes tailored to each piece of video on the fly. The key is to have that built into the content, which until just lately has not happened very much due to inertia. Buying, installing, and maintaining AFD inserters costs money, just like everything else.
And at best it is a workaround, and it is poorly implemented most places or not at all due to that inertia. Its been around since 2006, but change moves at a snail's pace unless there is sufficient motivation. There hasn't been any until lately, but the recent proliferation of non center-cut safe HD commercials is starting to change that. If enough advertisers produce framed for 16:9 and broadcasters chop their graphics off making the advertiser not want to pay them, things will start to change in a hurry.
There is one more solution, which is to just simply outlive 4:3 TVs, which most of us have already done by upgrading to HD. Eventually SD viewers and their equipment, will just die out. Cable and sat will support them until the bitter end, until they make up only about 2% of viewers, and then pull the plug. And the transition will then finally, 3+ decades later, be complete.
