How sure are you that they switched because of themes? Did you see user research? I left because of its poor performance, and MySpace was no substitute for friendster; it targeted an artsy demographic. But Facebook was.
Yes. I worked in social networks 15 years ago. It was a heavy research topic for me.
You're a highly technical user. Non-technical people are weird - part of the MySpace exodus was the belief that it spread "computer viruses", really
There was more to the switches but I'd have to dredge it up probably through archive sites these days. The reasons the surveys supported I considered ridiculous but it doesn't matter it's better to understand consumer behavior - we can't easily change it.
Especially these days. It was not possible for me to be a teenager with high speed wi-fi when I was one 30 years ago. I've got near zero understanding of the modern consumer youth market or what they think. Against all my expectations I've become an old person.
Anyways, the freeform HTML was a major driver - it was geocities with less effort, which had also exited through a liquidity event and currently has a clone these days https://neocities.org/browse