Would fixing it improve their ad business?
I'm still surprised by how often people (not necessarily you!) forget about misaligned purposes: your purpose for using Gmail is to have a good email service; Google's purpose for running Gmail is to make money, _not_ necessarily by providing a good email service.
When purposes misalign like that, you get users bewildered about why such a competent company would be “incapable” of providing a less crappy service.
Compare with Thunderbird: they make money to pay the bills but no-one's getting rich. Their only way of getting money is by building a good email client — by building features that companies will pay them to build; or by making a general-purpose email client good enough that users will donate.
(I know Thunderbird is not directly equivalent because it's just a client, not an email server, but the email client part is comparable.)