No, it does not answer the question. Let's tighten the semantics down a bit more.
Why were some married men allowed to become priests in the Roman Church while most are required to take a vow of celibacy?
Are there any estimates as to the number of married priests that might currently exist in the Roman Catholic Church if they were permitted to wave their vow of celibacy and marry prior to ordination?
You wrote:
"No, it does not answer the question. Let's tighten the semantics down a bit more."
No, your question was answered. No "semantics" were involved.
"Why were some married men allowed to become priests in the Roman Church while most are required to take a vow of celibacy?"
1) No one is required to take a vow of celibacy. It is voluntary. All vows are by their nature voluntary. 2) The Roman Church decided almost a 1,000 years ago it was best to ordain unmarried men. 3) Those men in the Roman Church who are married priests are a special case (i.e. not raised in the Church, converts, with later in life vocations). They are subject to the Pastoral Provision issued in the 1980's.
"Are there any estimates as to the number of married priests that might currently exist in the Roman Catholic Church if they were permitted to wave their vow of celibacy and marry prior to ordination?"
Not that I am aware of.