A: "Hi, can you please supply us with 50MW for the next 12 hours?"
B: "Hi, can you please supply us with 2.16Tj at a rate of 50MW?"
Watt-hours, Megawatt-hours, and terawatt-hours are used because that's the descriptive term of energy actually produced.
I've got a good gut sense for what a 3 MW wind turbine looks like, so when I read "50 MW Plant" - I can already envision about how large, and about how many turbines it will have (approx 15-30).
TWh/year doesn't tell me as much, because the plant might be located in a very windy place. Or maybe not in a windy place at all - the data is still useful, but I prefer MW when people are talking about a plant's "physicality".