Transformers can, well, transform into cars, and that’s cool, but that’s their only real defining characteristic.
They look different, they have different weapons and attacks, which leads to more interesting battles.
Jaegers are just empty shells that are controlled by people, and Transformers are actual sentient creatures, but the empty shell is actually a more diverse and interesting mech.
When it comes time for the robots to fight in Transformers, the battles aren’t nearly as creative because the robots all have basically the same abilities, shoot guns and punch things.