A line has a limit on amount of characters it can have if 'text wrapping' is not enabled (can't be enabled in a messaging app).
Lets say the limit is 25 characters.
As example, you just typed a 23 character line.
Now you want to add the word limit at the end of that line.
The word limit has 5 characters, so it will not fit and be added to a new line.
Now if your new line ends with 25 characters total, then it will look longer than the previous line.
In order for all lines to be the same length, a word that exceeds the character limit at the end of a line would have to be split across the 2 lines by a hyphen (ie. lim-it). This behavior is usually seen in text editors as an optional feature in the settings.