Well seeing how xmas Pokemon are for a limited time it would make sense for them to be extremely rare. Now granted they are not rare as shiny pokemon, this gives you a better chance of finding one. Christmas season doesn't last forever so for everyone who has caught xmas pokes will have the decision of keeping their xmas pokemon, or selling them for a very nice price due to the season being over and them being no longer obtainable. I see that you are asking about a specific pokemon in general which is the "xmas swablu" This pokemon to me is the best themed looking xmas pokemon and can see why the rate on it is the way it is. Now there are other pokemon such as sentret/furret/pikachu/teddiursa/etc. that are common enough for people even on the earliest routes to obtain but still will take some time to find. as for swablu,eevee,etc. these spawn rates of the pokemon are already rare so encountering a xmas themed one will be very challenging indeed as it should be. I believe the rates are fine as it is and its all about grinding and just encountering the opportunity when it comes. "Hard work pays off" Gl though ^_^