I will say that football certainly is here in Southern California. Its still a very popular sport, but many schools have quite a few fewer players each year these days than 20 years ago. Some teams are having to combine their freshman and JV squads or make similar adjustments.
I think there are a lot of reasons why fewer kids are doing extracurriculars these days (including increasing social media, streaming, internet, cell phone and video game use). And contact sports like football may be impacted by safety concerns as we've learned more about head injuries — and band wouldn't suffer from those safety issues. But I'd be surprised if there aren't some general trends of declines in band participation happening nationwide.
I'm not saying that bands are in jeopardy of drying up completely. But assuming some level of decline, calling the legislator's statement that bands are on the decline "stupid" seems a bit dismissive as well.