Data is just the last thing networks are clinging onto to make extra money. First it was minutes when phones were just phones. At that time even though you could get virtually any phone for free on a 12 month 200 minute £30 contract, I remember the 'o2 max' 750 minutes tariff being £75/month
When SMS took off, most tariffs offered either no text (I remember 500 minutes and 0 text being a common combination) or 500 minutes and 100 texts because it was 10/12p a text after that.
Now it's data so unlimited/unlimited/2gb is what they tend to offer unless you pay more. They give you plenty of minutes and texts because that's not where the money is. If the problem with unlimited data really was people abusing it and running whole home networks off it etc then the easy answer would be change unlimited to 50gb