Using one or the other is often a matter of taste, prior knowledge or other factors. Plus that Plesk is definitely stronger in WordPress management that includes also staging/cloning/sync, automatic security and mass management of sites.

That Plesk is mostly Windows is completely wrong. Plesk was originally built on Linux and only later a Windows version was added - and both versions are rock solid today. Plus that the Plesk install base is 90%+ Linux based. Windows is only a minor part of the Plesk servers out there.