Why So. Korea not the US in buying military hardware?

All of your arguments make sense to me! I also keep wondering why?

The only reason I can think of is maybe there is a little bribe under the table from SK to whoever OKs they purchase.

Yes it should be made here. That way The Philippines could provide more employment for Filipinos (more money to the economy) but also income selling the products to other countries.

2 main reasons to buy the SK fighters, politics and price. The FA-50 are an excellent fighter trainer, something like a poor man's F16, costing much less, and are brand new, with many modern features. In a dogfight or combat situation the FA-50 just slightly out performs the older F-5 fighters last flown by the PAF. It takes a lot more skills to fly and maintain an older cheaper aircraft like the F-5; and much more skills to maintain a more advanced aircraft like the F-16. The US basically concluded it would be a bad idea for the PAF to think about flying the F-16 or more advanced fighters at this time, because it is very unlikely the PAF could maintain them. The FA-50 gives a lot of bang for the buck, and avoids problems with older or more complex aircraft, it is an excellent choice, and a good fit for the PAF. imho, the PAF should also buy a bunch of cheap older fighters, just to get maintenance crews and pilots back in shape. The PAF should also form aircraft maintenance crews to service USAF jets, this is a highly profitable business, since the USAF outsources most routine maintenance to civilian contractors,

Secondly is politics. Anti-US pro-china quisling have most filipinos believing the propaganda that used US military equiptment is junk, so any mention of this stirs up a lot of negative emotions. This is very funny because even rich nations often buy used US ships, planes and other hardware, like Taiwan that purchased 2 decomissioned frigates this year. Beligerant filipinos would complain that the frigates were old junk, and blame the old junk for thier weak navy, lol. This theme comes up often, even within the AFP, ie: the reason why it took weeks for the military to mobilize to typhoon disaster releif was because all their helicopters, ships, etc were 'old junk' from the US, thus filipinos often use this convenient excuse to dodge thier own incompetance or weakness.

The reason is mainly political and it makes a lot of economic sense. Buying an aircraft with that capability needs US congress approval and it might get derailed, washed down or delayed, just as other countries experienced. Buying Korean speeds up the acquisition process with much better financial deal and the spare parts could come faster with no political strings. The FA-50 could be fitted with the latest US and European avionics and armaments so it is a win-win for the Philippines.

Making those planes locally will make it more expensive because extensive tooling work requires volumes. Twelve planes is way too small.

FA50 is assembled in SK , but it uses many U.S. parts, for example GE engine.

Half of it is made in U.S. It is not cheap.　It is accident‐prone. The Philippine government will regret that choice immediately.