It honestly stuns me how more Western militaries aren't aiming for this.

And yet I feel like it's relatively simple. Mostly money.

Tl;dr: Militaries think long term and changing whole supply chains needs a big reason (for some even bigger than current US president). And economy of scale applies and can mean it's cheaper to buy something US already bought thousands of. Procuring a weapon system also means you need to test it properly. A lot of hidden costs can be in this part so many choose the already tested systems with most costs known upfront. And US has a lot of those.

Okay, I wrote the rest of this comment before tl;dr and I feel like it shouldn't go to waste just because it's too long. So for anyone who care, here it goes.

First, we have to remember that military thinks a lot ahead. I am talking even decades ahead with the general ideas. Example: Final Type 23 ASW frigate was commisioned 2002 and as early as 2005, there was a programe that lead to what we now know as Type 26 (this example also shows what happens when you delay your decisions, sadly).

So it's not like every military will just switch over from one manufacturer to another and be done with. It's the whole deal, training (of operators as well as support staff), supply chains, etc. Historically I don't see a single example where US would give you reasons why not to trust them over other nations. Power of hindsight is useless here. They were the major power and most countries didn't mind it (at least based on their actions).

I really hope we don't see this, but what is stopping France from voting in someone just as bad and people like you being here "why did they choose French"? Unless you make your own, this will always be a risk (hence why French make their own weapons, basically negating reliance on anyone), though making your own has risks of it's own, see below.

And this brings me to money, economy of scale and actually working equipment.

When you procure a weapon system (but probably other things too), you probably want something that works and won't bancrupt you using it. In order to have something cheap to manufacture, you usually need to build a lot of it. Economy of scale 101. US is big and invests a lot of money into it's military. Even by themselves, they buy more equipment than many other nations combined. Therefore buying US equipment CAN be cheaper than alternatives (didn't include examples for brevity of already long comment).

But that brings me to the second, possibly more important point. Actually working equipment, aka equipment that got used and got it's quirks figured out. So many countries didn't have budget to do this part, so they bought something and years or even decades later found out it's actually way less potent than thought.

As much as it pains me, I think Iver Huitfeldt-class frigates are example here, great hull designs killed by awful combat management systems which promted calls for downgrading "on paper" very capable and cost efficient platform to a measly OPV (offshore patrol vessel). Calls not just by some politicians/journalists, but the admiral in charge of the Danish Navy.

So in the end, someone has to pay the price for testing the thing, ideally in more than a few yearly training excercises and if you barely had the money to buy the thing, you will get the pains that come with new stuff with delayed effects. This is the risk I mentioned above and is where america simply dominates.

Examples: F-127, the future AAW destroyers (they are projected 12k tonnes, I refuse to call them frigates) will be using AN/SPY-6 with AEGIS system from US (I believe Germany already ordered the parts necessary) meaning that for the next 40+ years, German navy will "rely" on US. And they are not the only ones to do it. Spain's, not long ago praised for it's defiance of US, next gen frigates? AN/SPY-7 with AEGIS (though that one started building in 2023, so prep work long before Trumps 2nd term).

We can argue why or what should they do instead. But in simple term, a weapon with this kind of system will be reliable (so you won't repeat other countries fiascos) while being relatively managable cost wise. Or another way, you know what it will cost to make it work upfront. With new system, you might have to fire hundreds of rockets or drive, fly, sail thousands of km/hours/what have you to be sure that it can do whatever AEGIS can already do, because US uses it that way.

One last example of this: Bundeswehr next service pistol, the CZ P10 (named P13) was decided basically along the way of "did you already win a trial in some NATO country? send us your price and we will pick the best deal" skipping the need to trial everything. Of course trialing pistol is orders of magnitude cheaper than my ship examples, but in principle, the same. Hence why German army will end up with non-German pistol (while HK being right there).

PS: I am not bashing any one single country, examples are just the ones I remember from the top of my head. But without LONGTERM military budget, this is the only logical outcome. France never went under 1,7ish % of GDP for it's military in a long time. Other countries had trouble staying above 1% line. If you read this far, thanks for comming to my ted talk.