Choice in the matter
Would you prefer to tailor your breakup if you had the option? Would you want the individual to break up with you to ask how you would like to break up? It may be a decent idea in theory. However, when you consider it, it doesn’t make sense.
We can assume that the recipient flew off the handle very quickly once they received this note. Because this is essentially a breakup note in and of itself, receiving this message is effectively taking away the option. This isn’t something we want to happen.