Eventually, I realized that it was because the devs wanted to put "AWS" on their resumes. I wondered how long it would take management to catch on that they were being used as a place to spruce up your resume before moving on to catch bigger fish.
But not long after, I realized that the management was doing the same thing. "Led a team migration to AWS" looked good on their resume, also, and they also intended to move on/up. Shortly after I left, the place got bought and the building it was in is empty now.
I wonder, now that Amazon is having layoffs and Big Tech generally is not as many people's target employer, will "migrated off of AWS to in-house servers" be what devs (and management) want on their resume?