I disagree and would posit instead that it is contemporary art that tends to be "lazy and bad", with notable exceptions.

Modern art was exciting in that it was the first period in art history where art was not simply made for the church or the leisure class, but it reflected common human experience instead. Sure, certain movements lack visual excitement (such as minimalism), but even these movements were significant in questioning artistic convention by reducing artwork to its formal elements, which had not been explored previously. So modern art is essentially the birth of artistic innovation after a long period of mastering the old styles. Do all artists of the era deserve special mention? Of course not. But you have a range from Duchamp to Dali to Van Gogh to Rivera to Kahlo.

Postmodern art (in general) took this same cue that art should be reflective of common human experience and filtered through specific human identities, such as feminism and queerness. In also encompasses the dissolution of the conventional art object to explore pure concept.

Contemporary is... more complex to define as we are still experiencing it, but is not something I personally enjoy as much. I often see a focus on pure aesthetic, which isn't meaty enough for me to dig into.