I've also seen many people who keep a gmail or other mass market account
as a professional address knowing that they will move between
institutional addresses. As companies come and go faster and people
transition between them more often, keeping a semi-permanent
professional contact point is a sound strategy.
Can these people really be confident that "gmail.com" will outlive their
professional life? At the very least, they should use their own domain name -
even if they use a GMail or Yahoo Mail-type service to host their email. (As
an extra benefit - to keep this message on-topic - the email that they send
won't be subject to DMARC.)
The fact that such services are useful is undeniable. As is the fact that
"@yahoo.com" and "@gmail.com" email address look unprofessional. They just do.
Ross.