i get this question alot. there is, obviously, very little in scripture that will say ‘when John 6 and the ‘last supper’ talk about eating Jesus body actually for real in the eucharist, it means just that. you really eat His body and blood, which has been transubstantiated from bread and wine.’ if it did, protestants would believe it. but since it doesn’t say exactly that, they don’t.
however, there ARE several questions that arise from the protestant view -
one - the scripture does admonish us to partake of ‘communion’ worthily, by examining ourselves first. it says that if we eat unworthily, we eat and drink damnation unto ourselves. now, this doesn’t make alot of sense if it’s only a symbol. it’s kind of a bum deal. if you do it RIGHT, all you get is a symbol. if you do it WRONG - damnation. ?
two - if Jesus only meant it metaphorically, then why didn’t He explain that when all of His disciples left Him (except for the twelve). ‘this is a hard saying, who can accept it?’ would have been a good time for Jesus to say ‘i mean this metaphorically.’
three - why did the church, from the LATEST 70 AD, teach that it was truly the body and blood of Christ, all the way to the reformation, if it wasn’t? wouldn’t someone have spoken up, who lived when Jesus did, and said ‘hey - it’s just a symbol’?
it’s basically a matter of faith. if you have faith that Jesus established the church, and that the ‘deposit of faith’ and the ‘keys to the kingdom’ are inextricably entwined in the Tradition and magesterium of the church, then you accept its teaching about the eucharist.
if you don’t accept this Tradition, and only believe what the Bible says, then you will probably (though not necessarily) reject the concept of transubstantiation.