Amplitude belongs to Sony and for that reason and various others, Harmonix says it has to be a PlayStation exclusive.
The thing you may have noticed about successfully Kickstarted video games is that a lot of them are for the PC. It's a natural fit - if you're on the Kickstarter site, then it's very likely you're on your PC, or at least know where it is and how to turn it on - and so it's natural to ask why Harmonix, which launched a Kickstarter for Amplitude earlier this month, didn't include a PC version of the game in its plans.
The short answer is that it couldn't. "This is Sony's IP and taking it to non-PlayStation platforms is just not in the cards right now," Nick Chester of Harmonix told Rock, Paper, Shotgun. "Going into this, we knew how the lack of a PC/Mac/Linux version might have an impact [on our Kickstarter]; we're not blind to that fact, as I've seen some suggest."
Hopes for something down the road in the way of a "spiritual successor" seem faint too, as Chester added that the complications go beyond the simple question of Sony owning the IP. "There are other moving parts that wouldn't necessarily give us a clear path to doing a spiritual successor on other platforms without the Amplitude name," he said.
The built-in support for Amplitude obviously comes from Team PlayStation - the original was a PS2 exclusive, after all - and so it's hard to gauge how much of an impact the promise of a PC release would have on its fortunes. But it certainly couldn't hurt, and Amplitude could use the help: With four days left in the Kickstarter, it's not even halfway to its $775,000 goal.
Source: Rock, Paper, Shotgun