Why does eviction paperwork and process have to be followed to the letter?

Because there are laws protecting renters, to insure they are properly notified, with enough time for them to react.

Any type of legal paperwork follows a very formal format and regimented filing process.

Because making someone homeless is a BFD.

If the word in question is relevant it’s important. Even the words “the” and “a” are very meaningful.

It is grounds for a dismissal.
If you spell a persons name wrong and you go to court the defandant can say “that’s not me. My name is Jon not John” and you have to start all over.
Since it can take 30 days or more just to get a court date you don’t want to do ANYTHING that will force you to go back to square one!
disclaimer, I am not an attorney but I have owned and managed rental property in California for over 25 years.

I should also add that even though I’ve done this for so long I still use an attorney for evictions because I want to be sure every eye is dotted and every t crossed.

Because that’s the way the law works, for everything. It has to. The wording on legal papers must be exact to minimize the margin for errors and/or abuse. A friend of mine once got out of a quite deserved traffic violation because the officer wrote the wrong time on the ticket. It was like 12:30 AM, but he wrote it as 12:30 PM.