There aren’t, and an increasing number of reasons it probably is.

It’s just been such a gradual process of discovery, much of which predated the explosion of the computer age, that we have an anchoring bias preventing us from seeing it. We think “well no, the universe has always behaved this weird way, that’s just a coincidence it’s similar to what we’re starting to do in simulating our own virtual worlds.”

How different might Einstein and Bohr’s argument have been around if the moon existed when no one was looking if they were discovering the implication that it might be the case in a world where nearly every virtual world with a moon has one that isn’t rendered if no one is looking at it?

In antiquity it was assumed that the world was continuous because quantization of matter was an impious insult to divine design. It was a huge surprise that people took very hard when it was experimentally shown to be quantized. And then the behaviors were so odd - why was it going from continuous to discrete only when interacted with? Why did it go back the other way if you erased the information about the interaction?

Would this have been as unusual if we’d already had procedural generated virtual worlds generated with a continuous seed function but then converted to discrete units in order to track interactions by free agents determined outside the seed generation (such as players or AI agents)? Would the quantum eraser have been as puzzling through this lens when we’ve seen how memory optimizations would ideally discard state tracking data for objects that are no longer marked as having changed?

A lot of the weirdness we’ve discovered about our world makes a ton of sense through the lens of simulation theory - it’s just that the language with which to interpret it this way postdated the discovery of the weirdness by nearly a century such that we’ve grown up accepting that weirdness as normal and inherent to ‘reality.’

And just to be clear, absolutely nothing in our universe can be shown to be mathematically ‘real’ and everything is either confirmably mathematically ‘digital’ or indeterminate (like spacetime). And yet people are very committed to calling it real and disturbed at the idea of calling it a digital world.