> Non-monotonicity in particular seems like a bad property of a voting system, so I'm confused that IRV is so popular recently.

Same here. The idea of lobbying for a voting system where your vote for a candidate might hurt them, or where you might be better off not voting at all than expressing your honest preference is bizarre to me. If IRV was the only alternative, sure, but we have multiple other systems which don't have as bad tradeoffs. STAR or Ranked Robin would be so much better, but the Equal Vote Coalition doesn't seem to have the power behind it that FairVote does.