Aside from people with a single Gmail account (and perhaps 1 work email where they have to use Outlook anyway), who can deal with logging in to multiple webmail

Aside from people with a single Gmail account (and perhaps 1 work email where they have to use Outlook anyway), who can deal with logging in to multiple webmail apps, all different to each other? An email client keeps the experience consistent across all accounts. It integrates with whatever workflow and desktop you have. It's cheaper to run. It's easier to use. It's faster. Probably uses less CPU and RAM.