These fans allege that he's noticed how Yamada's family environment isn't that great (her mother works too much, perhaps, neglecting them?) so he wants to keep Yamada in the restaurant where she is happier.
Hm...I'm far more inclined to think that Souma just thought it would be amusing to keep them apart...until, as happens with anything involving Yamada, the lutz inadvertently gets turned back on him... (^___^)