How has the phrase the "Mecca of some activity" originated and not the "Rome" or "Athens"

Merriam Webster explains that a mecca is:

a place regarded as a center for a specified group, activity, or interest

Mecca is a sacred place in Islam. Wikipedia writes:

Mecca is regarded as the holiest city in Islam.[3] More than 13 million Muslims visit Mecca annually, including several million who perform the Hajj (pilgrimage).[4] As a result, Mecca has become one of the most cosmopolitan and diverse cities in the Muslim world,[5] however, non-Muslims are prohibited from entering the city.[6] Mecca and Medina and its surrounding outskirts are the only two places where the Quran was composed.

As Take Our Word says,

English uses it in such a figurative sense because Mecca is the birthplace of Muhammed, making it the ultimate pilgrimage place of Muslims.

So to go to Mecca, for a Muslim, is to go to the "Holy Grail"--it is the ultimate religious destination. Rome and Athens are older cities, but they do not hold the religious, spiritual meaning that Mecca does. They are old destinations, but they are not the endpoint of a religious group. Because Mecca is the place which Muslims must make a pilgrimage to, it has a different religious connotation than Jerusalem. Thus the phrase uses Mecca rather than another city.

In addition to being a holy city, Mecca is s pilgrimage target. The most common uses I've heard of "X is the Mecca of Y" are about going to X, e.g. qualifying to compete at Wimbledon. So the salient feature is that you go there, as opposed to the city just being important as a commerce center, capital, etc.

Actually while all the logic above seems plausible. The only reason Mecca and not any other city is used is because the usage was restricted to what would be classified as 'vices' by the Christians like alcohol, gambling etc. It was much later that it became a common usage and lost it derogatory aspect.

So it was done because this was where all the Muslims used to gather: at a time when European powers were fighting Muslim Turks throughout North Africa and taking over Muslim ruled India. Thus the intended meaning was Mecca = center of vices or where all evil men (supposedly Muslims) go or face while praying.

Funny how bad meanings end up being good ones. (Nothing against Muslims: just quoting etymology not endorsing the view point.)

This Ngram suggests the phrase became popular during the 19th century.

The OED says of mecca:

A place regarded as supremely sacred or valuable, or where a faith, policy, truth, etc., originates. Also more generally: a place which attracts people of a particular group or with a particular interest; a resort of (also for) a certain group of people.

Their earliest is quotation from the The Southern Literary Messenger (1843):

Wander in thought with me o'er the Mecca of Protestants, and linger, for a moment, around the graves of Luther and Melancthon [sic].

I found an earlier example in A Collection of Voyages and Travels published 1704:

The generality of the Inhabitants these Islands are Heathens; but from Sanxil to Samboangan the People the Coast are Mahometans; more particularly in the Islands of Basilan and Xolo, which are as it were the Metropolis that Superstition and the Mecca of Archipelago; because the first of it is bury'd, there of whom the giddy Headed Casikes tell a thousand Fables.

This, like other early uses, is describing a place as a religious centre of activity for an unfamiliar people, and perhaps Mecca was used rather than Rome or the Vatican as it suggests, for the Christian writer and readers, a non-Christian otherness or unfamiliarity.

Later, usage spread to non-religious centres of activity or especially pilgrimage and congregation, such as from The Spirit of Times (1877):

This is the Mecca of hundreds who desire to regain shattered health, and to breathe the pure mountain air so invigorating to weak and consumptive invalids.

Or The Guardian (2006):

Yet even these achievements are topped in my estimation by a claim once made by this newspaper. "Ashton-under-Lyne," it proclaimed "is the Mecca of tripe-eaters." (Or possibly tripe-lovers; this was a long time ago.)