Webmail vs Thunderbird......an Anal-Retentive Type makes a Comment
"...Because most of the world has gone to webmail, especially Gmail...."
Anal-retentive types (like me) have an email archive on a machine which I control going back to the year 2000. So I can retrieve what I received and sent over the last seventeen years. Note that this archive comprises email managed by multiple providers.
Anal-retentive types (like me) don't want Google (or anyone else) having this capability. And even if Google or others do have this capability, it would lock me in to using their service, something else I would wish to avoid.
Pity about GCHQ and the NSA, but then there's absolutely nothing I can do about them!!
PS I quite like Thunderbird.