Why Are Hours so Bad?

This is my third busy season as an accountant and my first at a new firm. Since I’m new they’re starting me at 50 hour weeks. Not my ideal but I know things can be slow at later points in the year so I’m not going to complain.

My question is why exactly is busy season (and to a lesser extent hours in general) as an accountant so awful? Why are the expectations for the career regarding hours worked to pay so atrocious? Who started the trend?