I get why Bayern would get the hate, It's the biggest kid on the block. Why does Hoffernheim create hatred?
Hoffenheim got bought up and money-bombed by Dietmar Hopp with the millions he made with SAP. It's not really different from how RB Leipzig got pushed.
There are also several local teams that have been successful in the past and have been more popular and established with the local populace, namely SV Waldhof Mannheim (Bundesliga 1983 - 1990), VfR Mannheim (Champion 1949) and SV Sandhausen. The old football fans who have been struggling to support their local teams have been very angry with that guy on his high horse suddenly appearing and throwing bags of money at a random village team no one had cared for until then.
It didn't help that Hopp baited financially struggling SV Waldhof with a loan that essentially turned it into a vessel club that scouts, grooms and is then forced to hand over its most promising youth talents to Hoffenheim.
More hated than FC Bayern and Hoffenheim? Doubtful.