It has been announced that Starship will need 16x launches to fully refuel the Lunar Starship.
A bunch of accountants have determined that one very specific mission profile under very specific assumptions based on current capabilities of a development prototype will need 16 launches.
Elon Musk has already clarified that it is going to be more like 8, maybe even only 4.
why isn't the Starship already fueled when reaching orbit
Because it burns the fuel to get to orbit.
why will the tankers have fuel whereas the Starships to reach moon or mars will not
Because the Lunar Starship which goes to the Moon has 100 tons of stuff in it that needs to go to the Moon. The Tanker Starship has 100 tons of fuel in it that goes to the Lunar Starship.