My first guess is 2012 lacked easily accessible hardware accelerated h.264 encoding on the host and the cheaper clients lacked easily accessible hardware accelerated h.264 decoding. Now you can find hardware accelerated decode in your $20 IoT device.
Piggybacking off that, OnLive never seemed to know if they were a hardware company, a software company, or a cloud company, and depending on which exec was talking and the day of the week seemed to have a different focus each press release.
Today you have major players that already cover all three bases (Microsoft and Sony) interested and playing in the space. You also have more opportunity to see minor players enter the space with less of need to be hardware companies (because more users already have capable hardware devices), or cloud companies (because more commodity streaming cloud options are available than ever before on AWS/Azure/etc), or even software companies as more platforms including the web platform have increasingly more high level APIs for a lot of the building blocks of game streaming.
Maybe pricing arbitrage? Every gamer I know has like 20-30 titles in their queue they want to try out. To purchase all of them only for a few moments play would be prohibitive. Pay per use makes more sense if it falls below current gpu cloud cost (~$1/hr).
What's amazing is that if you can deliver video games at 4K 60fps. You can deliver all but the most intensive any application this way.
but they couldn't make it work commercially and shut down in 2015.
Bandwidth hasn't really gone up, so what will be different this time round?
Edit: they actually laid off all employees in 2012, then relaunched and still failed in 2015