Because it costs a lot of money. AM as a system is way more expensive than FM.
It's cheaper to either have an FM translator or refer people to your mobile app.
Let capitalism work
I am sure if anyone did do something, it would be the best they can do economically. Letting successfully funded AMs (or any business) take advantage of opertuntires is basic economics. If buying a translator is best then that's the way to go. There is no one size fits all in radio.
In areas of good ground conductivity a decent AM signal will let you get around the 15 mile 60 db rule. If you move a 1 kw station below 800 khz from above 1400 it should push the signal much farther. You might get an extra antenna height for a translator.
Every Station no mater what band needs web exposure.