What happened to his career?

Yes, I AM talking about Biehn's performance, not just the character. He is the reason Reese had that radiance and intensity about him. He's the reason I bought everything Kyle Reese said and why I am able to suspend disbelief when I watch the film.

Contrasting that with say, Nick Stahl's John Connor from T3; nothing he said about Judgment Day affected me. This catastrophic event that the core of the story has forever revolved around seemed more like an after-thought most of the time. I never felt that sense of urgency that this mortifying event was coming like I did when Biehn created that imaginative vision of utter purgatory when he talked about it.

For me, not just anyone could've pulled that off.

https://www.quora.com/Whatever-happened-to-the-actor-who-played-The-Terminators-Kyle-Reese-Where-is-he-now

everybody in showbiz is easily replaceable

He's played some legendary characters from legendary movies. Maybe he turned down Weinstein, or some other satanic Hollywood elite?

https://www.hollywoodreporter.com/heat-vision/terminator-what-happened-star-michael-biehn-1228634

Essentially, wants to spend time with his family and isn't motivated by fame or money.

Sounds like a cool guy to share a beer with...

He reminds me of James Franciscus.

Both were rugged, handsome and in several big budget action films but never really hit that A-list leading man level.

Biehn’s other problem was being mostly an action film guy. I can’t remember seeing him in a traditional dramatic role.

He should have tried to get into an indie picture of some kind. Maybe he could have gained more dramatic credibility or some hipster value.

He was removed out of the Alien 3 script. That's the biggest problem. He never got a proper career boost in the 90s that would have kept him relevant.