Unfortunately, standardization != widespread use. Tracking pixels are still the most reliable way to know whether a recipient (or many) opened your message.
Gemail, Outlook.com/hotmail, thunderbird and outlook all block images, unless whitelisted... Now, there may be other providers/clients that don't, but the above accounts for a significant number of users (if not most western mail users).
That's not a good excuse for not implementing a standard. It's also a little like saying "private investigators are still the most reliable way to know whether a person is at home": it's true, but not really a better thing to implement.
