if you are conservative and believe someone has a low they aren't folding and you have to improve to a straight or better to have a winning high hand and only count the diamond flush as a winning flush
then you require 2 players to pay pot to see showdown. either both splitting the low, or 1 with a winning low and one with a losing low or a losing high.
for calling the turn pot bet to be +ev.
if you aren't as conservative then its much easier for the call to be +ev. and its possible its +ev without any additional $ going in on the river.