No politician wants to be the one to make the case to shut down the factories that produce these things, even when the military has advised Congress to do so [1].
[1] https://www.washingtonpost.com/business/economy/the-end-of-t...
Instead we have jets we don’t need, and tanks sitting in a desert unused.
Two words: metal fatigue. Every airframe only has a finite amount of hours it can fly before its structure becomes too weak. Fighters in particular that regularly perform high-g manoeuvres. So they have to be replaced anyway.
The war in Afghanistan saw Western militaries burning off airframe-hours at a phenomenal rate using expensive fighters designed for neer-peer conflicts to drop dumb bombs, when you could have done the job for a fraction of the cost with simple propeller planes like https://en.wikipedia.org/wiki/Embraer_EMB_314_Super_Tucano
The problems with the F-15/F-16/F-18 is that Chinese and Russian missiles might be able to shoot them down more easily than the F-22 or F-35, since the F-22 and F-35 are stealthed.
The problem with the F-22 and F-35 is high unit cost, so they can't have as many as they'd like.
It's also possible that their stealth might not work so well on future Russian/Chinese radars, for example they might use different frequencies. You can be sure both those countries are working on countermeasures to stealth aircraft.
Possibly the solution will be an unmanned aircraft. This would be able to pull >10g manouvers, which aircraft with a pilot in can't.
what's wrong with just using the jets we already have. I mean we have like a gazillion of those things. what percentage of the military/armed forces is currently being used or has been used over the last 10 years. I'm guessing it's a very small percentage.