Depends on how the content was provided, I'd guess. AFAIK, stations are loathe to mess with content that's been provided to them lest they make a mistake and forfeit any money they would make off it.

So my guess in this situation is that the commercial was provided to the station as a 16:9 spot delivered in a letterboxed SD 4:3 file. So what do they do? They run it as a 4:3 spot, no nevermind that the content is 16:9.

Now, you might think, "well, that's stupid. Why didn't they just crop it and run it as 16:9?" Number of reasons. Sometimes the content is actually 4:3 and contains information or some kind of graphic or something in the black space. If a station cropped out the phone number/website for an advertiser you can bet that the advertiser would demand restitution, and might reconsider working with this station in the future.

Also sometimes they're baked in up-stream. Local stations only get so many advertising spots during national and syndicated programming, and if the show is delivered with a commercial already like that in it, they have no right to edit it. Plus it would mean having to take the whole show into a system, making the changes, and then kicking it back out to be slipstreamed into the programming. That's a lot of effort for a 30 second spot, plus there's the risk that in the process it could degrade any information on-screen, like fine print. No way a station would want to risk that.

And beyond that, stations get a lot of commercials, so QCing and editing them all like this would add a lot of time and work to what is likely quite a busy workflow already. And since they station doesn't get any extra money for making these changes, and assumes a fair amount of risk in the process, it's just not worth it.