He did it because he understands that nothing he ever does in his life is likely to be as much fun or as much of a challenge as pitching in a Major League game. So here he was at 49, back from Tommy John surgery, the second-oldest pitcher to start a Major League game. Heck, he's 10 years younger than Satchell Paige was said to be when he got his final start in 1965.
When Rockies general manager Dan O'Dowd sent his first scout to see Moyer throw last winter, he was skeptical of the glowing report that came across his desk. So he sent another scout. And then another.
"Every guy came back saying the same thing," O'Dowd said. "They don't know how he's going to physically hold up, but he doesn't look any different than he did before he got hurt."
That's the thing that gets lost in the buzz about Moyer's age. He has never been a guy who threw hard. He first learned a changeup when he was at St. Joe's and was always a guy who relied more on location and movement than velocity.
He was 45 years old when he helped the Phillies win a championship in 2008, and before he got hurt in 2010, was still getting Major League hitters out.
The Rockies wanted him, first, because they were absolutely convinced he could still get hitters out. And they wanted him because of his smart and relentless work ethic, because they believed he would be precisely the right guy for their slew of gifted young pitchers to learn from.
Moyer got to this point by pitching superbly in Spring Training, and then on Saturday as he walked out to the bullpen to prepare for his 629th Major League start, he was confronted with the meaning of it all.
"I had a lot of things running through my head," Moyer said. "But I think once I was able to get out and start doing some running and play some catch, it was all baseball. It was a very good feeling, a feeling of where I've been before. It's a place I love being."
You know how this story has to go. Actually, there's only one way it can go. That's for Moyer to pick up where he left off on July 20, 2010, and win his 268th game. He would be an inspiration on so many levels, and then he would keep on going and give us one more thing to love about sports.
Don't you just hate it when real life gets in the way of a perfect story line? Jordan Schafer, who was born 80 days after Moyer's Major League debut in 1986, led off the game by slapping a 76-mph slider over the right-field wall, and the Astros were off and running to a 7-3 victory.
Moyer sailed through a couple of innings after that home run, spotting a 78-mph fastball here and a 69-changeup there. He got Carlos Lee to ground a 78-mph fastball weakly back to the mound in the first, struck out Brian Bogusevic on the same pitch in the second and got Chris Snyder on a 71-mph changeup in the fourth.
But it wasn't the night he'd hoped for. The Rockies made three errors, and when Moyer left a 76-mph fastball over the plate, Astros left-fielder J.D. Martinez lofted it into the left-field seats in the fourth.
Moyer ended up going five innings and allowed five hits and four runs, three of them earned. He was out-pitched by Astros right-hander Lucas Harrell, who tossed seven shutout innings for his second Major League victory.
Afterward, Moyer said he'd passed every test physically and was pleased, even on a night when just one of his 69 pitches cracked the 80-mph barrier.
"Physically, I feel outstanding," Moyer said. "That's a good sign for me. I think my last outing in Spring Training, I threw just over 100 pitches, so I felt very strong. I'm pleased with that side of it. I felt very comfortable with where I was tonight. It's been a long time since I've been there. It's where I need to be."
Moyer's second start will be Thursday at Coors Field, another moment in this improbable road back. Down the hallway, the Astros, one of baseball's youngest teams, said the evening had been both an adventure and a challenge.
"It's the most comfortable 0-for-4 you'll ever have," Astros catcher Chris Snyder said. "The guy keeps doing it. He's done it this long because he knows how to pitch with what he's got. We got to him a couple of times when we needed to tonight, which was big, but if he settles in and he's really spotting up, that's when he's at his toughest."