They probably should be; I've smacked and broken more than one myself.
If you can find accident reports involving crawlspace lighting, or carefully word a proposal, you may be able to get protection on crawlspace lights. Shock and electrocution are not the dangers that having sharp, hot, broken glass in your face/head are imo. I dont think it a bad idea but then again, here, crawlspace lights are an afterthought and done as cheaply as possible. There's usually one at the entrance and one near an HVAC unit, if it's lit at all.