This used to be the default option! I still remember the WWDC keynote where the feature (called Resume) was introduced. Having it on by default made for a really cool demo, where all the windows were restored after a restart:

https://youtu.be/LPMjUtfQPks?t=19m16s

Not only was it on by default, there actually wasn't an easy way to turn it off, leading to tips like this:

https://osxdaily.com/2011/07/18/disable-mac-os-x-lion-resume...

I'm not sure when the option was added or when it stopped being on by default.