You have to be a little bit more specific than that and quantify and itemise the «many» part. Otherwise it is pure speculations, generalisations, arm chair theories and hand waving.
What is a «vanilla system»? A brand new laptop? Then the hardware is likely faulty, and Apple will replace the faulty computing contraption or refund the purchase. A brand new install on an existing laptop? Likely a hardware fault, a compatibility problem (less likely) or, indeed, a specific or unspecified defect in the software.
I reboot my laptop approximately once a quarter – when a new update or upgrade is released. The average uptime is 3 months. I run a uninterrupted succession of OS X updates and upgrades dating back into 2009 – when I begrudgingly switched away from my Sony Vaio Z17 business laptop running Linux due to the X server randomly crashing on and bricking Vaio Z series laptops in-flight or upon an awake with no available recourse. I have not had to reinstall OS X from scratch even once and still occasionally come across non-OS files on the file system being intact since the original 2009 install. Different kernel versions in between 2009 and now have crashed on me less than ten times. The laptop goes to sleep and then wakes up daily. Zero maintenance. I used to have to reboot it once a year to disable the CSR mode, but not anymore – the stuff just works (except when I need to run dtrace / dtruss which is a less once in two years activity now). Clearly your vague definition «many bugs» does not apply to me.
I can't say the same about the said Vaio laptop that I still happen to have around, and that is in a perfect working condition (sans the obsolete 32-bit CPU and maxed out 4Gb of RAM). It runs a version of Ubuntu but every upgrade is still a gamble. A upgrade to Ubuntu 20 has bricked the laptop in the umpteenth time, and it now requires an autopsy and a full reinstall via booting it from an external eSATA drive via a PCI Express card attached to it.
This isn't handwaving. I'm talking about bugs in the software (not hardware) with rdars attached. For some of them the bug dates back to like 10.5 or so, and the fix is straightforward, but it just hasn't been done. For others the problem is harder (but still possible) to reproduce, but the buggy component is managed by what has been described to me as "one of the somewhat less competent teams" at Apple, with a track record of "extremely stupid design decisions".
Describing them in more detail will deanonymize me so I'm not going to do that.
