The reason those numbers are so low is because of the hoops jumped through via NFA and the tax.

I'm sure there's some truth to this but they are still not in common usage among firearm owners and the average American would not think about a suppressor before going and shooting which means it’s not “universal” or “held more or less without reflection or argument”.

If you had to fill out extra forms, go to the DMV a second time, and pay an additional fee for seatbelts, most people wouldn’t have them in their car despite them being common sense safety equipment.

Maybe. Some people were very resistant in the US when seatbelts first became mandated in all vehicles in the US in 1968, however it wasn't;t until the 80s when most of the laws mandating their use began. Today, since they are both required in all new vehicles in the US (some exceptions apply) and their use is required by law they would now be “universal” or “held more or less without reflection or argument” in the US.

With the change at the end of the year to the NFA tax suppressors might follow the same trend but I doubt it. Just like with seatbelts, the majority of people will probably ignore them unless they are required to use them.