1)Everyone can and everyone does it. Its called ghosting.
2)Because its not free neutral structure like OKW or ost trench, it costs resources, just like bunker and you can't enter it, just like bunker.
Just so you know, wehrmacht commander that gives trenches does cost resources for him to build. And it's free for all bar with drinks so all happy people can use them.
British pub trenches don't understand people who don't yell Ding Ding.
You have around 6 seconds to move your units before the bomb hits. The noise is loud enough to completely move out of the way before it hits. Adding smoke would just be nonsensical, as the noise is already a clear indicator of where the bomb will land.
Once you hear it, you should move every single one of your units in the vicinity. There is ample warning and time to move your units.
Relic has never addressed this in the past because it really doesn't need to be. It's still expensive at 160 munitions, and it doesn't unlock until the very late game. I don't see any real issues with it.
If you're complaining about air recon, that means it is costing the German player 240 munitions to bomb a single target. Recon is not free.
Also, the Stuka bomb is only available to four commanders, and only two of those have air recon - Jaeger armor and Close Air support.
You forget Luftwaffe commander which has the only loiter recon plane option. (This commander is not close air support)
222 hp buff, will make them much more useful, when they don't die instantly when somebody throws rocks at them. Hell it feels like 222 take more damage from infantry shooting at it than kubelwagon...