No Stupid Questions

You have to understand that in the pre-classical era, Roman people had minor god cults throughout their small villages, and the Greeks did the same thing. The cults beliefs did some traveling over time, and reasonable people slowly began piecing together a shared mythos.

Over time, as the Greeks pulled together their culture into a power structure of loosely associated city-states, their religious cults from dozens and dozens of villages all were glued together into a more cohesive pantheon.

Romans then adopted and 'latinized' the Greek pantheon, mixing in several of their own superstitions and cults.

This means you will have a God of creation and a God of that pond over there, which might have later been rationalized into a nymph.

EDIT:

It's much the same in the Abrahamic religions. Yahweh was the god of storms/thunder, sort of second or third in command to El, had a wife etc. Later he was given domain over war and then later promoted to the one true God.

You can see small remnants of this in the Bible, in the conflicts with Baal (another diety of the pantheon) especially (theorized to be some of the oldest stories in the Bible). Yahweh often uses thunder and lightning in his signs, and in older records mention is made of his wife/children etc.

Before things were commonly written down and literacy was common Religious beliefs were messy, constantly adapting and re-adapting to changing times, rulers, and encounters with other systems of belief.

List of Roman Deities

This includes such high profile gods and goddesses as Devera, who blessed the brooms used to sweep temples, Laverna, goddess of charlatans and theives, Lua, who specifically existed to have weapons captured in war sacrificed to her, Picus, an Italian god of woodpeckers, or Salus, goddess of specifically the welfare of people living in the city of Rome.

How much more specific and unknown do you want to get? There are plenty of surviving deities from the Roman era who have no surviving function that we know of.

I'll just point out that monotheism creates some interesting and silly problems too. The Pegans can just assign fertility to a female god for example. Without that option, monotheists have to shoehorn the concept of fertility and birth into the patriarch god.

This is the genesis of the idea of men's spunk being referred to as a "seed". It was "common sense" in Western civilization from Roman times to the 18th Century that sperm contained fully-formed little people. Women were just the dirt where you planted those little guys. The inventor of the microscope studied sperm first. And he fully expected to find homoculi in his spunk.

Meanwhile the "primitive" people's of the world would have found this to be insane. Babies come from women, stupid.

The Greek ones are older than the Roman ones. Jupiter = (Zeus + pater) * a couple of sound changes, where pater = father. It's my favorite fact.

It's conceivable that the Greeks also copy and pasted their cannon of deities from whatever was en vogue at the time. I doubt there was a process. A story was created, it somehow stuck in the zeitgeist, and a century later through a game of telephone, Bob was elevated to be god of hemorrhoids.

The Egyptians had a lot of gods for everything. Moses had to beat the poly-deity lifestyle out of the Israelites with stone tablets. The heathens in the North of Europe had concocted their own family of gods. If you go even further afield, you'll find more and different gods.

They all kind of had a father big boss figure and then a complicated network of subs. If you have no printing press and no microwave ovens, humans naturally gravitated to stories like that to make sense of the world. The systems grew organically.

How do Catholics choose their patron saints? Same deal.

How do modern people decide what to wear. Whats cool or in fashion at the time. The sun, the moon, lightning. Never goes out of style.

St. Hubbins: the Patron Saint of quality footwear

I figure the same reasoning was used for all of those patron saints as well. Or maybe it just evolved naturally as people need to see something bigger than themselves.

i wonder what the most obscure god was

They did not choose.

Wasn't it basically tourism?

From what I understand, household gods were very common — personal traditions about a small god that perhaps your family worshipped for generations and had a small shrine to for protection. Some of these were picked up and developed into more general purposes for a larger audience.

The Romans in particular also had a habit of picking up local deities for a larger pantheon, in these cases less of choosing gods, it was more like reducing some gods with very elaborate lore down to just a few specific traits. Though of course some gods were invented by storytellers on the spot and picked up.