Where does it say this?
My problem is that HEC in Pakistan are taking too long to attest my Bachelors degree because my degree was. completed 10 years ago and I have to hop through a lot of red tape to get it done. I have a masters degree from the US shouldn't that be sufficient for WES EE credential assessment requirements?
There is clearly some big confusion on this page regarding WES assessements and required documents.
Yes, you CAN have only your Masters assessed, or Bachelors only, or BOTH... It's up to you. For maximum points, you are only required to assess to highest one. HOWEVER.....
For some particular countries/schools/programs of education you attended, WES may ask you to provide your previous degree documents (i.e. Transcripts & Diploma), even though you didn't initially request it to be assessed.
For example, if you had a Masters done in France, they'll just ask you for documents for that particular degree.
But if you had say a Bachelors done in Morocco, they will automatically request your high school documents (Transcripts/Diploma), even if you didn't want it assessed. In fact, it won't even show up in your final report (unless you want it to), as it is just to confirm that you fulfilled the pre-requisite.
Who knows why they have these requirements for some countries and not for others.
So, in your particular case, you should be able to have just your Masters degree assessed. But if the system asks you to submit documents for Bachelor, do it. If you don't, your evaluation will go ON HOLD until you do.
Cheers.