There is a short answer to the above question. It is down to his throwing. Sean Cronin offers so, so much in the loose - he runs as if he is shot out of a cannon. Remember this burst against Montpellier back in 2011? It isn't an exaggeration to say that this is one of about 100 motoring breaks in Cronin's career.
But the notion that he develops the throwing yips from time to time is a hard one to shake. Take last year's clash with Wales at the Millennium Stadium. Ireland were three from three in the Six Nations and going for a Grand Slam. A lineout 5m from the Welsh line with the clock ticking down.
Luckily for him there was a Welsh knock-on and he got a reprieve but it was another black mark against the Limerick man's throwing. Unfortunately for Cronin, he sometimes misses his man.
But to say that he has been omitted from the 23 for today's game - after a memorable cameo off the bench last weekend that saw him obliterate a Welsh ball carrier - because of his throwing is to say that the two hookers selected ahead of him are far better in that regard.
They are not.
Sean Cronin must be wondering what he did to get dropped from the bench. Made a good impact last week.
— Rúaidhrí O'Connor (@RuaidhriOC) February 11, 2016
Ireland captain Rory Best has struggled throughout his career at lineout time, much like Cronin. Best's Lions test chances were submarined in 2013 because of his throwing inaccuracy during the warm-up games. His strengths lie in other areas - mainly his scrummaging, rucking and ball carrying.
Likewise Strauss isn't known for his sure-fire throws under pressure either. In Joe Schmidt's final season as Leinster coach Strauss overthrew Leo Cullen in the Clermont 22 in an away game that blew a costly attacking platform.
I don't bring up two isolated examples of his rivals' missteps solely to buttress Cronin's credentials but merely to illustrate that all of the hookers at Ireland's disposal are afflicted by similar if not identical lineout-throwing woes.
Strauss at his peak - during Leinster's two-year run as European kings - was arguably the best of the three but right now Cronin should definitely be in the 23. Rory Best isn't just picked for his lineout throwing - his contribution around the park is a massive plus too but it seems that Cronin's marauding runs aren't valued similarly.
He was curiously dropped out of the 23 halfway through the World Cup.
That was a head-scratcher.
He battled his way back into the squad last week, played as well as he could have and is now out again. Questioning Joe Schmidt's team selection always makes you look thick.
But this is just plain wrong.