I think you are underestimating how many people watch games in places/conditions where they cannot here the TV sound.
I understand what you are saying. But, these days, I am working where NOBODY can hear the sound from the TV. My audience is those 275 mommas, daddies, grandparents, brothers, sisters, aunts, uncles, and cousins in the stands on Friday nights. Once in a while, we get a 3K - 4K audience. TV? Ha.
Yeah, OK. The local in-town school district broadcasts the Thursday night game (and I get my share of those). They have a field mic. But, virtually the same audience. If Nielsen did a survey of townsfolk on one of those Thursday nights, I dare say they might show a 0.0 share.
No. It ain't TV folks that I'm targeting. It is the butts-in-the-seats. They bought a ticket, and they deserve to know what is going on. SOOOOO much better to be able to explain with a verbal announcement - along with a signal.
Yeah, I had my day with 15K to 70K in the stands, and on TV - somewhere - every week. You are right. Those guys slugging down a hot beer in a cheesy dive somewhere ain't gonna hear the announcement. Signals are helpful for the most rudimentary fouls. But, using S21 for a disconcerting signals foul ain't gonna make sense to a visual-only audience. Can't do anything about that. But, a field mic within a stadium can help tremendously.