Not just that, you have all your emails with you, even without internet, even when aws/azure/cloudflare/... fails, plus you can write replies and everything else while offline and just send/sync when you get internet access (eg. on a cheap flight with expensive wifi).

Many things don't need an app, a web site is enough (and they somehow force apps onto us), but email, especially with something like thunderbird is a great thing to have directly installed on your pc (or portable with you).