High level American athletes seem to taking a backseat to foreign fighters for 3 reasons imo.
1. Highly athletic Americans play other sports and make A LOT more money playing those other sports.
2. The UFC is purposely looking to sign foreign talent so more eyeballs are on the UFC globally. The American UFC market is pretty much set. It's just smart business to look to open up other markets.
3. Sean Strickland said it best and it's one of the few things I actually agree with him on: the 10K/10K standard UFC newcomers contract is terrible for American fighters. They have to get a 2nd and 3rd job just to survive. Let's say they win. That's 20K. Gotta pay your gym/manager 20-30% of your gross income. That's 5K. Then you have to pay taxes on your gross income. That's about a third. So about 6.5K. That leaves the fighter with a net income of about 8.5K for about 3-5 months. Depending on where you live that's not enough to live for 3-5 months. Between rent, car note, insurance, food, and other monthly living expenses that fighter would be in debt without a 2nd and possibly 3rd job.
Now take a foreign fighter that on 10K/10K. In a lot of places that fighter can move good off that 10K/10K life. They can live a upper class life off that because American money stretches WAY farther outside of the USA and Europe. I have a really close friend that retired from the army, moved to the Philippines and lives in a legitimate villa with 6 rooms, 3 bathrooms, a pool and it's a walking distance from the ocean for $700 a month. He spends less than $50 a month on food to fill up his fridge. Dude is living like a king at 39 years old off an army pension in the Philippines.
Anyway I'll get off my soapbox now. And before you ask I visited him this last November and had Thanksgiving there. Yeah I almost didn't jump on my flight home.