I think the reason might be twofold - one, they don't believe the proof, no matter how compelling and historical, simply because it contradicts what some esteemed RC (by them) wrote on a blog or in a book. And, second - though this is sinister and I hesitate to say it - some KNOW the truth but care more about roping into Catholicism someone who doesn't or simply to denigrate a "Protestant" every chance they get in hopes of converting someone out. Either way, it shows an abysmal lack of integrity coming from those who think they are superior to others in the faith. I pray sincere seekers of truth see through the facade.
It is stunning, even dumbfounding. How could there be so much brick hard denial? Yet too, this pretense of their arguments never having been shown to be less solid than they need to be to actually fly is like kabuki theater played out for possible audiences who have not yet seen it -- and those who have seen it but not followed things closely enough in the past (like -- the typical casual reader?) will be continued to be lead their way, gambling the continued empty assertions, denials, distractions & bluffing will save the day.
If it is motivations that could be spoken of -- instead of necessarily trying to rope anyone in (though there is a bit of that all along) it seems to me to be more intensely focused along lines of self-reassurance, and keeping the rest of the RC sheeples in line with the common present-day RC apologetic -- no matter how many times and in how many ways significant elements of that has been falsified, if only just in part, but falsified enough to need the argument to be entirely reworded.
It doesn't help matters that the history of many things do not lay in straight lines.
The apologetic continually attempts to present itself to be that way (straight), but it is a crooked path on the best of honest days because there were human beings involved, all along each and every path...
There is where the mystical/magical "the Church will never err" type of thinking then kicks in (while identifying "The Church" as being the Roman Catholic one, etc.)--- needing to compartmentalize any troubles or contradiction -- and through painstaking massaging and application of special pleadings and unequally, inconsistently applied measurements of comparison, arrive at the place where no matter what --- "they" (an infamous "they", again) can tell themselves every OTHER ecclesiastical body has erred and is wrong, but not the one with the Roman Pontiff.
Even the original source of the word "Pontiff" has to be ignored -- or else accepted as "that's how God wanted it to be".
Pontifex Maximus -- the (Roman Empire) Emperor. They back off from that now... but keep the "Pontiff" portion.
Ratzinger wrote of misunderstandings due to the Orthodox, the Roman Catholics and the Protestants speaking differing {theological] languages...
I understand the RC language. Few Roman Catholics seem to understand ours. They claim to, and point to converts among themselves when doing so, but then don't seem to recognize the circular reasoning, the special pleadings, and all the needing to look at it "just so" to make it all appear to work.
Or else if they do know our 'language'-- they don't post much on THIS forum [the following said in stage whisper]--> and I can't say I blame them.
For if they do much acknowledge ANYTHING that may go counter to RC apologetic, if they don't at the same time overwhelm that same admission with reams of something, anything to attempt to invalidate or limit what they just confessed to -- then katy-bar-the-door -- their co-religionists will come after them with teeth sharpened.
Meanwhile, what occurs but relentless efforts to force unconditional surrender (to the claims their own ecclesiastical community makes for itself) enforcing that on whoever can be either cooed at or else intimidated, with those immune to either then being insulted one way or another in order to set up pretext for later attacks on whomever would dare to agree with those who challenge particular Roman, resisting both the smiling invitation, and all the intimidation (which used to include threats of extermination).
Is THAT Jesus? Is that the way He goes about His business? For long centuries Rome did seem to say, yes, if it comes to that. Fall in line, (fall at our feet --even kiss the pope's feet as per pope Gregory VII) or suffer for not doing so --whichever way we choose.
I think I understand how that sort of thinking evolved to be. I could trace some of it, even through the scholastics --- but my, oh, my how long (and how many words?) would it take to tell the story?