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I'm tired of the anti-3.3V logic arguments. What does commodity even mean?
It means, many electronic components work only with 5V signals. Especially ones for handling high currents.
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What does standard even mean in MOSFETs?
The voltage required to switch the MOSFET. That's individual and can be extracted from the data sheet. There are only few which do at 3.3V and even fewer of them can handle 50A and up, which is required to use it for switching the 15A of a heated bed without additional cooling.
All this can be solved, of course. But it makes electronics more complex and more difficult to assemble. RepRap is about DIYers, ya know?
If complexity doesn't matter to you, feel free to pick an Intel i7. Waay faster than any ARM.