People have already mentioned they liked how he was a mirror to the WoL's own adventurous self and they connected emotionally with that, but I liked how straightforward his goals were and how unapologetic he was about pursuing them. I felt like the whole Elpis arc tried waaay too hard to make us be friends with Emet, and bent over backwards to portray him as a tragic, misunderstood victim of circumstance. It left a bad taste in my mouth, and Zenos' selfish pursuit of his own wants to the detriment of everyone around him was an incredibly refreshing contrast to that. It's also a much more grounded motivation- even if you don't like or respect Zenos, you can still understand him in a visceral, instinctive way that doesn't require twenty hours of exposition.