The web map is entertaining to watch

https://tar1090.adsbexchange.com/

I think the issue is that military is permitted to fly without broadcasting anything, but the airspace is restricted to avoid civilian collisions. Or maybe de-facto clear by staying in high enough altitudes?

I have seen some military aircraft light up while practicing refueling over the pacific, but go dark when leaving or returning to base.

OpenADSB and ADSBExchange will definitely give you a better view of any military and private planes broadcasting ADSB.