I'm about 10 years past using email clients. I would have to guess most of this audience is, too.
Compared to gmail accessed via web, email clients offer slower startup, higher bug count, inferior search tools, a crazily confusing configuration burden, create a deep disincentive to access email from any machine but your own, a centrifugal bumble-puppy model for where your emails reside that can be relied upon to place the emails "on the wrong machine" (or none at all, or N-fold on each of M machines) when you need it most, and they bifurcate your message store when you change jobs or ISPs, etc. Moreover, I am spared the horrors of the aged hacks and platform-bound kludgery intended to address the above faults (e.g., IMAP or whatever Office thinks it provides).
Email clients are the landlines of the 2010s.