Because every Wednesday morning they both like to roll over and play dead.
Only real problem I have with windows 10 is the forced defender in the background always on. Even if you tell it not to "scan" your drive it still runs and scans other things. This has caused issues for me. Some games I play use third party anti-cheat-anti-hack software that tries to protect memory locations. Defender and those applications don't mix. Which just locks up that memory location usually and ends up in a massive memory leak. Had it corrupt a drive a few times as it screwed over the pagefile setting for that drive after my system ran out of 64GB of memory when playing a single game a few times.
Once I changed the registry setting to kill defender for good, no more problems like that.