Regardless of the fact that he is "playing within the rules", it looks awfully bad to the average voter and he is experiencing a backlash in the polls.
Has it occurred to you that maybe the RNC is coalescing behind the scenes for Trump. (They may be corrupt, but they're not stupid.) That maybe they are publicly pushing Cruz so that he will alienate voters and ruin his political viability not only for a possible 2020 run, but for his own reelection as Senator.
There is little to no evidence that the RNC is coalescing behind the scenes for Trump.
I think that is the point behind nearly every NeverCruz post.
Steal the election by challenging Trump delegates and replacing them with Cruz delegates at the state conventions and the voters that gave Trump the victory in that state or district will be angry. The only way to make them more angry is to then prove to them that the theft was all okay by the rules.
It tells the voters that their vote, and in essence their opinion, doesn't matter. A lot of them will just stay home in November, since their party has told them their vote doesn't matter anyway.