Do you actually know - and have the appropriate backing from precedent - or are you just guessing? One thing I've found out about contract law is that it doesn't look anything like you'd think it does just from reading the things you sign, so it seems to me that it's very easy to make mistakes in this area without realising them if you just sort of read it in a tourist-y fashion from time to time.
Yeah, because you would actually read & physically sign an employment agreement, and that agreement actually has some bearing on how you relate to your job. OTOH an EULA is not read by most people, and their enforceability has been challenged in court. https://en.wikipedia.org/wiki/Software_license_agreement#Enf...
You can't sign your rights away, and "we own all of IP you produce past, present and future," is a forsaking of rights that would naturally be exercisable by the person signing the contract.
Employment agreements are also subject to contract law concepts such as consideration[1], which would come into play when someone stops and asks "what's in it for me?" A single job as described at the beginning of the relationship through the employment agreement is probably not going to be seen as valuable enough for someone to have legitimately signed away his future productivity.
