We don't currently know the reason, but it may have been to make the name stand to more and to make an otherwise forgettable Pokemon slightly more unique. As of Generation 8, Farfetch'd and Sirfetch'd are still the only Pokemon with apostrophes in their names. You can argue that without an apostrophe, it would look more awkward. That may be true, but Feraligatr and Victreebel also have letters cut off, so it was probably more of a design choice than anything else. The deveopers may not have wanted a real word for a Pokemon, but Gloom, Seel, and Mew exist.
Overall, we don't have a definite answer. The most likely reason is a more unique name, but it could have also been because of awkward letter placement or the decision to not have another real word as a Pokemon.
