It is all part of learning your space and playing your role.
If you are trying to interject on the responsibilities a person overseeing a defined by ELT functional area or established formal role with a customer; that person indeed should not engage you.
Not sure what it is, perhaps generational.
Know your role.
Play your role.
Only certain parties are in roles defined by management to perform critical functions; based on their proven experience and managerial sanctioning.
The way critical business is ran is not through consensus.
Sorry that is reality. Tough lesson for those early in career.
Stop thinking that people are mandated to care about other's opinions or perspectives. Their non-engagement should be telling you something. Play your role.
Sorry.