Why do none of my Pikachu have the option to evolve into Raichu?

Solution 1:

The clone Pikachu, available through the photobomb from February 26th until 2nd of March 2020, was also not able to evolve. They have a different black marking on their ears, as shown in the following picture (clone on the right):

Probably you are trying to evolve one of these, which is not possible. You should be able to evolve non-event/non-clone Pikachus. One that you obtain today (or a non-event caught before the photobomb-clone-event), would be evolve-able to Raichu.

Solution 2:

These are Event Pokemon.

Event Pokemon (at this point in time) do not have anything special about them, other then appearance, and potentially a special move. The most recent versions of the Event Pikachus either wear a party hat, or are "Clone" Pikachus, as part of the Armored Mewtwo Event.

The main difference is that the Clone Pikachus have a zigzag black tip on each ear, and cannot be evolved. The normal Pikachus have a flat black tip on each ear, and can be evolved.

This is a part of the Pokemon Day event, that celebrates the re-release of the Mewtwo Strikes Back movie on Netflix.

Remember Clone Pokémon? Well, some are coming to Pokémon GO! In celebration of the Pokémon Day launch of Pokémon: Mewtwo Strikes Back—Evolution on Netflix, special Clone Pokémon — including Venusaur, Charizard, and Blastoise — will appear in four-star raids. Be sure to use #GOsnapshot during the event, too — Clone Pikachu might appear in your photo, and you might be able to catch it!

These are specific to the "Character" Pokemon from the movie; the reason why this Clone Pikachu doesn't have an evolution is because it is modeled after Ash's Pikachu, that never evolves throughout the entire Pokemon series.