Linux on its own isn't even 0.1% visitors normally. We're talking multiple orders of magnitude less for disabled mitigations. And on top of all that, it's possible that exploiting on that machine is going to be harder due to custom software with uncommon memory layout - i.e. it's probably not a stock Ubuntu. And finally, for accessing data outside of the page, you really want to have some specific target, so they'd have to guess that too.