Diesel locomotives can't deliver enough power. The power rating of the diesel generator on most locomotives ranges from 2 to 4 megawatts. The combined power rating of motors on high-speed trainsets range from 5 to 20 megawatts, depending on size and design speed.

Diesel engines are rated for maximum power, while motors are rated for continuous power. Motors can deliver much more than their continuous-rated power for a few seconds. This means much greater acceleration, and much greater power requirements, than any engine could provide.

Diesel locomotives can't deliver enough power. The power rating of the diesel generator on most locomotives ranges from 2 to 4 megawatts. The combined power rating of motors on high-speed trainsets range from 5 to 20 megawatts, depending on size and design speed.

Diesel engines are rated for maximum power, while motors are rated for continuous power. Motors can deliver much more than their continuous-rated power for a few seconds. This means much greater acceleration, and much greater power requirements, than any engine could provide.

Note that aerodynamic drag, which is the dominant resistance on all but the slowest trains, is proportional to the square of speed.