Most flight data recorders log AOA as a parameter and AOA features in a lot of accident investigations. All airliners have a AOA vane as part of the stall warning system and certain FBW aircraft use it's input as part of the control law configuration. Accident reports frequently mention high AOA, but wht don't we get a display on the flight deck?
Cost! My A320 FCOMs show an optional AOA guage on the instrument panel, but to my knowledge no operator has ever fitted one. And until enough reports state that one factor of an accident was an increasing AOA which the pilot wasn't aware of and they become mandatory, they won't be fitted.
The Tucano in RAF service has an AOA guage and an AOA indexer. Unfortunarely, the indexer is not calibrated to the approach speed of the Tucano in RAF service and is not much use. And use of the guage was not taught. But after losing my ASI during an inverted spin one day (a regular problem until a restrictor was fitted in the pitot line) I was forced to use AOA against power as an approach reference. This made me realise the value of the instrument and I used it regularly from that point.
Some airliners have the ability to display a Flight Path Vector on the Primary Flying Display. The difference between your attitude and the FPV is you angle of attack. The A320 SOPs for my airline requires use of the FPV for visual flying and Non Precision Approaches. It's a very useful tool.