[af_vet_1981]

Now why exactly do Catholics apply the title to priests who are but man then?

The Apostles used the word "father" in the New Testament to apply to men. They do not, however, ascribe to them that which only belongs to God (My father, my father, the chariot of Israel, and the horsemen thereof.).

I write not these things to shame you, but as my beloved sons I warn you. For though ye have ten thousand instructors in Christ, yet have ye not many fathers: for in Christ Jesus I have begotten you through the gospel. Wherefore I beseech you, be ye followers of me. For this cause have I sent unto you Timotheus, who is my beloved son, and faithful in the Lord, who shall bring you into remembrance of my ways which be in Christ, as I teach every where in every church.

First Corinthians, Catholic chapter four, Protestant verses fourteen to seventeen,
as authorized, but not authored, by King James

[Elsie]

...yet have ye not many fathers:

HMMMmmm…

Worldwide. Worldwide, the number of priests in 1970 was 419,728. In 2012, there were a total of 414,313 priests.

While the total number of priests worldwide has therefore remained about the same since 1970, the Catholic population has nearly doubled, growing from 653.6 million in 1970 to 1.229 billion in 2012.

Priest shortage in the Catholic Church - Wikipedia

https://en.wikipedia.org/wiki/Priest_shortage_in_the_Catholic_Church

[Elsie]

For this cause have I sent unto you Timotheus, who is my beloved son, and faithful in the Lord, who shall bring you into remembrance of my ways which be in Christ, as I teach every where in every church.

(Though I don't know what the HELL has gotten into those 7 Catholic churches in Asia!)