It's called resume driven development, and the reason it's done is because it helps those who do it get jobs
Doubly true if you're not all-in on one of the major Bigcorp silos (Java, C#).
I occasionally check their LinkedIn and they're still spending 12-15 months every time at companies, being CTO or Big Data Strategist or whatever.
Mostly good experiences when it's a specialist gig that happens to require a specific technology. Like some parts of a stack aren't interchangeable and aren't easy to pick up overnight.