I would guess that none of them ignore it, or at least you wouldn’t see it. On IFR the controllers automatically keep them clear and on VFR they won’t be on radar flight following anyway. Anyone who busts them (assuming they can be indentified) gets violated later by the FAA, so they don’t get another chance. Pretty strictly enforced!
You might know the difference, but for benefit of other readers: SUA includes but is not limited to Restricted and Prohibited airspace. Aircraft can go through those with approriate ATC authorization, which might not happen a lot, but does happen. Some of these areas (maybe even most) are not active all of the time and usually have altitude limitations. You wouldn’t know from watching FA whether they were authorized or not, active or not, or how high they extend. For example, even the notorious Washington ADIZ only goes to, but not including, FL180 (roughly 18,000 feet), but at that altitude you must be on an IFR flight plan and ATC can send you right over it.
SUA also includes alert areas and Military Operations Areas (MOAs) which anyone can go through VFR at any time but should simply be vigilant for the special operations. It may not always be wise, but it’s not illegal. IFR traffic are automatically vectored clear of active MOAs. Then there are Warning areas that would be Restricted, but are offshore and therefore outside the US jurisdiction. And probably a few more that I’m not mentioning.