There are two big issues with the writing in Act 3, at least from my perspective.
The first issue is the aforementioned spelling, grammatical, and editing mistakes. Things like character lines truncated by string errors (so they're missing the first or last letters of the sentence), malformed escape sequences (like n\ instead of \n) breaking formatting, missing punctuation, and the like all contribute to breaking my suspension of disbelief. If I have to take time and effort to decode what somebody is saying, it pulls me out of the world, and that's a big no-no in any kind of fiction.
The second one - more subtle but no less problematic - is the loss of character voice. In creative writing, each character should have a certain manner of speaking. Things like verbal tics, diction, accents, and the like all help sell the illusion that this is a real person, not an excuse to time-gate three pieces of mediocre hentai. If those are missing, especially after having been established previously, it is VERY jarring... and also breaks suspension of disbelief.
Take, for example, the difference between these two lines:
"Hero, you must come with me at once! The empire is in grave danger!"
"Come with me you must save the kingdom"
They both convey the same meaning: The player needs to go with the NPC, with the implication that if they don't the kingdom will fall. The former, however, tells us a little bit about the speaker: They're likely an authority of some kind (as who else would speak to a fantasy hero like that?), and the phrase 'grave danger' (a slightly more formal turn of phrase than you'd expect from a commoner or peasant without an education) indicates that the speaker has some schooling. Combine the two, and it's entirely reasonable to imagine that some robed figure is about to power-walk into the room the PC is currently occupying and dish out a big juicy quest. We don't even think about this kind of thing consciously, at least not for the most part. It simply gets filed away in our minds as another way to recognize a person.
In Act 3, this starts to fall apart. NPCs stop using their idiosyncrasies and start speaking "generically." Punctuation gets missed so they all come across as robots. The party banter, which previously was one of the parts that really made the world feel alive, comes off as wooden and stilted as a result.
We go from "Come on, $PLAYER, let's go home" to "We should go back to the castle" and it's just... bland.
So yeah. That's why I care about writing in games.