Because while Cath teaching insists that the bread and wine no longer exist after the presto-chango words of the unScriptural Cath priest, despite the fact that, in reality it is real bread, and thus like the real incarnated Christ, it looks, feels, behaves, etc. and would scientifically test as real flesh.
And thus it decays or is physically destroyed by some natural process, at which point Cath teaching holds that it is no longer Christ). However, since the bread and wine ceased to exist then that which decays does not exist as either bread or wine nor Christ.
Perhaps as "Christian Science" teaches, if these gluten-intolerant people could be convinced that what makes them sick was not reall then they would be fine. For in this issue, as in "Christian Science " (falsely so-called) matter does not exist, all is spirit, as pertains to the "real presence" under the appearance and testable properties of bread and wine.
While within Gnosticism you had the belief that what Christ looked and behaved like, as manifestly being incarnated with a tangible real body of flesh and blood, was not real (Christ being a sort of phantom but looking human), in Catholicism you have the belief that (in transubstantiation) what Christ looks, feels, tastes and would test as (bread and wine), is not the reality (Christ's corporeal body and blood only looking like bread and wine). And conversely, that the bread and wine is no longer real but only looks, feels, tastes, etc. like the real thing.
See post 369 and its links for more, by God's grace.
Does that help?
Yes, that was very interesting. I note, as you’re no doubt aware, that children with gluten-intolerance become extremely ill after receiving the wafer. It wouldn’t be lack of faith, or other theological issues, in their case. It’s just their body’s inability to process gluten. (I’m noting this in agreement with what you posted, btw. I realize that those who actually need to answer my question ignored it—and understandably so.)