Are both the Porygon's evolved forms, the Porygon2 and the Porygon-Z always omitted in the Pokémon anime, which is because of the incident of "Electric Solider Porygon", the episode from the Pokémon anime TV show?
The reason why we hardly ever see Porygon or any of its evolutions is because of the 1997 Japanese Seizures incident. If they put Porygon's line into any future episodes, it would create quite a controversy and bring back bad memories of the aforementioned incident. In other words, they're not going to feature Porygon again and take that risk.
I mostly agree with Mii-kun, the main reason why Porygon2 and Porygon-Z never got seen in the anime was due to the seizure incident with Electric Soldier Porygon that resulted in over 6,000 children getting hospitalized with symptoms of epileptic seizures.
If Porygon were to be shown in the anime now, it would have caused controversy and bring back bad memories of that incident so they decided it would be best not to showcase it or its evolutions in the anime again.
Well, guys? How many times are both the Porygon2 and the Porygon-Z ever mentioned in the Pokémon anime?
They haven't been--possibly because of the same reason. And considering the fact that Porygon hasn't been mentioned either I'm going to go out and assume that they won't be mentioned at all. Their one second movie appearance is all that we'll be getting to say in the least.
As others already mentioned, Porygon2 and Porygon-Z never made anime appearances because of the Electric Soldier Porygon incident; they only cameoed in movie 15. Porygon2 also appeared in the Johto Pokérap. In other words, Porygon2 was seen/mentioned twice and Porygon-Z only once.
I doubt that they'll ever make an episode with Porygon2/Z just because of the seizures incident...
But I believe they have no right to do this, I've seen many cartoons that have flashing scenes similar (or even worse) than the one in ESP, just because a number of individuals suffered from seizures during a certain episode doesn't mean Porygon should be wiped out completely from the anime... :\
The reason they didn't wipe him & his evolutions from the games should be the same reason why they shouldn't wipe him from the anime, simple as that.