Shouldn't a USB-C port have enough power delivery for a 5.25" drive? Or do the external drive enclosure manufacturers not want to step up the 5v to 12v?
Assuming you mean 3.5" instead of 5.25" (as you wrote), no. Probably not.
USB-C is able to provide up to 3A of 5V, eg up to 15W. But that's not universal, and many devices are not capable of supplying that maximum.
Even if it were universal: 15W is a little bit less than what a fairly-normal 3.5" drive needs to get spinning, so there's not enough power available (no matter how it is sliced and diced with voltage conversion).
"But that's just existing drives! Certainly, they can produce a drive that spins up slow enough that it fits within USB-C's power constraints!"
And certainly, that can be done. But there's still more mass to accelerate in a 3.5" drive than in a 2.5" drive, and that acceleration will always require more power (Joules). This matters for portable devices (which often run on battery).
Even once spinning: All else being the same, it takes less power to keep a smaller platter spinning than it does for a larger platter. It also takes less power to accelerate a smaller head actuator than it does a larger head actuator.
"But what about USB-PD? My phone charges with dozens of Watts. Why can't a hard drive use this, too? What if we cast aside power efficiency and yeet this thing together?"
It absolutely can be done. Anyone is free to create USB-PD computer accessories. Some people may even be able to use them. But since USB-PD availability is anything but universal on host ports, and is even less-universally understood, that limits compatibility from "works everywhere" to "works sometimes" and the support costs (and negative reviews) will be through the roof -- unless it is very selectively marketed to niche players who know exactly what they're doing.
It doesn't even seem like it would be particularly challenging to create for someone with the right skillset. And yet, there appear to be zero consumer products which operate this way.
USB-C is able to provide up to 3A of 5V, eg up to 15W. But that's not universal, and many devices are not capable of supplying that maximum.
Even if it were universal: 15W is a little bit less than what a fairly-normal 3.5" drive needs to get spinning, so there's not enough power available (no matter how it is sliced and diced with voltage conversion).
"But that's just existing drives! Certainly, they can produce a drive that spins up slow enough that it fits within USB-C's power constraints!"
And certainly, that can be done. But there's still more mass to accelerate in a 3.5" drive than in a 2.5" drive, and that acceleration will always require more power (Joules). This matters for portable devices (which often run on battery).
Even once spinning: All else being the same, it takes less power to keep a smaller platter spinning than it does for a larger platter. It also takes less power to accelerate a smaller head actuator than it does a larger head actuator.
"But what about USB-PD? My phone charges with dozens of Watts. Why can't a hard drive use this, too? What if we cast aside power efficiency and yeet this thing together?"
It absolutely can be done. Anyone is free to create USB-PD computer accessories. Some people may even be able to use them. But since USB-PD availability is anything but universal on host ports, and is even less-universally understood, that limits compatibility from "works everywhere" to "works sometimes" and the support costs (and negative reviews) will be through the roof -- unless it is very selectively marketed to niche players who know exactly what they're doing.
It doesn't even seem like it would be particularly challenging to create for someone with the right skillset. And yet, there appear to be zero consumer products which operate this way.