I can think of a lot of reasons for it.

• The machines take up a lot of space, and create a lot of mess.
• Pods have taken over a huge chunk of the pre-ground market.
• More people than ever have grinders at home.
• Packaging of pre-ground coffee is better than it used to be - better sealing containers, and fresher coffee to start with.
• The huge variety of coffee brands means that what you would get out isn’t what you put in.

There just isn’t much of a need for people who want to buy whole beans but grind them before getting home anymore. People will either buy whole beans and grind at home, buy ground coffee in a well-sealed container, or buy pods of some form.