This is a false premise. There is plenty of horrific abuse happening in small businesses, and at the local level. There are murders, rapes, and an endless stream of violations by management of their underlings. Evil exists at all scales.

However, the codification of certain motives–such as the alienating profit motive–encourages the otherwise less abusively included to collude in the ultimately exploitative program of their institution. The whole institution, then, resonates with this taint in outsiders' minds.

So, it's not that big always becomes evil, it's that "the bigger it is, the more likely you, u/bawana, will have heard of it."

Don't hesitate to read up on the ubiquity of "evil". I can get you started:

0. https://www.goodreads.com/book/show/224552.Why_Does_He_Do_Th...

1. https://www.goodreads.com/book/show/17601.The_Will_to_Change