How would forking occur? Forking requires copying data. Does the universe get cloned infinitely many copies all the time? That's quite an extraordinary claim.
This answer seems to be assuming the universe must be implemented on a classical computer and computed in a reasonable amount of time (that's not slowing down exponentially over time). That's not necessarily true.
I feel that assuming that the nature of how the universe is computed matches up with our first intuition feels a bit like the assumption in geocentrism that the universe matches up with our intuition of Earth being the center and the most significant body.
Even if you accept the basic premise of the universe being a simulation, there are still many ways it could work with MWI. The simulator's universe needn't have classical physics; the simulation could be running on quantum computers or something more advanced. Or the simulator's universe could be classical with a classical computer doing the simulation at exponentially-decreasing speeds as it has to simulate the increasing number of branches. It wouldn't make any difference to us how long the simulation takes to compute us, as long as the simulating machine doesn't break down and succumb to entropy. The simulator's universe could be something like Conway's game of life, and the simulation is running on a turing machine pattern which will never decay or break down. (I might be borrowing more than a few ideas from Permutation City here.)
Note that you're assuming that a nanosecond is a tiny amount of time. It's tiny relative to what we're used to, but as far as what "implements the universe" goes, a nanosecond could be enough time for a huge amount of occurrences to happen within. We don't know.
I feel that assuming that the nature of how the universe is computed matches up with our first intuition feels a bit like the assumption in geocentrism that the universe matches up with our intuition of Earth being the center and the most significant body.
Even if you accept the basic premise of the universe being a simulation, there are still many ways it could work with MWI. The simulator's universe needn't have classical physics; the simulation could be running on quantum computers or something more advanced. Or the simulator's universe could be classical with a classical computer doing the simulation at exponentially-decreasing speeds as it has to simulate the increasing number of branches. It wouldn't make any difference to us how long the simulation takes to compute us, as long as the simulating machine doesn't break down and succumb to entropy. The simulator's universe could be something like Conway's game of life, and the simulation is running on a turing machine pattern which will never decay or break down. (I might be borrowing more than a few ideas from Permutation City here.)