"For some reason their HR people must have received order to ignore the mainframers "
They aren't looking for "just mainframers"... they really want folks able to map from-mainframes-to-AWS...
As I've stated profusely in other threads... the average mainframer doesn't get the opportunity to do that... they are left to rot... the kids were given the new stuff, and refuse to learn mainframe...
So AWS has a problem finding these people...
Mainframers aren't trained on AWS... The kids with AWS turn their noses up on mainframes... and AWS isn't building these people...
I know one or two that have made that transition... older mainframers that jumped to distributed platforms decades ago and got lots of AWS certification... but they are rare...
So, same old chicken-and-egg problem, with no on ramp.
That is to say, no one to scalp from elsewhere that got trained and experienced on someone else's training dollars.
And well... few full time working IT folks on either side of the MF/AWS divide have the bandwidth to cram-learn the other platform and get the certs...