Mathcore is a euphemism used to describe talentless bands of the hardcore genre who use this term to fool you into thinking their inability to produce a coherent and catchy sounding rhythm was intentional. As such, mathcore songs are typically an amalgamation of riffs that don't sound well together with little or usually no attention paid to smooth transitions between them. Technical guitar work, complex time signatures, unorthodox chords, etc is just a more polite way of saying the band, especially the guitarist, sucks.
The Dillinger Escape Plan blows and anyone who says they like them does so because it makes them seem more "hardcore" and they want to impress their friends and other hardcore scene kids. Mathcore = sucks.