The majority of Pokemon that a trainer comes across will be found roaming their respective region's wild areas. There are nearly 900 Pokemon in the Pokedex, but they can't all be found in the wild. While some certainly can, some are much rarer to encounter on a stroll.
The allure of these Pokemon is their rarity and the challenge of legitimately obtaining one. Fans won't be opposed to more of them appearing in the wild, however.
Note: This article is subjective and reflects the opinion of the writer.
Top 5 Pokemon which don't appear enough in the wild
#5 - Eevee
For a long time, Eevee could only be obtained as a gift, either from NPCs or from the Game Corner. In later Generations, players can find Eevee in the wild, but it is still quite rare.
In Pokemon Sword and Shield, Eeveelutions appear in the wild pretty frequently. In Pokemon GO, Eevee often appears, too. In the main series games, it would be great if Eevee appeared more.
#4 - Smeargle
Smeargle is a very unique Pokemon, and has very limited locations where it can be found throughout the series. In Sword and Shield, Smeargle is completely unobtainable.
The Painter Pokemon is always fun to have on hand to battle other trainers or wild creatures. Smeargle could definitely benefit from more wild encounters.
#3 - Rotom
Rotom is one of the most diverse Pokemon in the entire franchise. It has several different forms, all with their own unique typing. Rotom has been a very popular competitive battler and even has a spotlight in the anime with the various Rotom items used by the characters. A plain, non-form Rotom appearing more often in the wild would be awesome.
#2 - Dragonite
In Pokemon Journeys: The Series, Ash and Goh come across an entire island inhabited by Dragonite and its pre-evolutions. Dragonite could not be found in the wild whatsoever until Generation V.
Even after that, it remains extremely rare to be found in the wild. It can be found wandering in a singular location in Sword and Shield's DLC, but it would be incredible to see a Dragonite Island added to the game.
#1 - Starter Pokemon
This is a package deal for number one. Starter Pokemon are extremely rare in the wild. Some games allow for starters to be caught, such as the Let's Go series. Other than that, all three starter Pokemon can typically only be obtained through events or trading methods. In the upcoming Pokemon Legends Arceus, it appears there are some starters found in the wild, which could be a good sign.