The commas are added to separate symbols The symbol | (Example: B = |3 ) is a “down-slash”, or “pipe”, and not a lower-case “L” or capital “i” The symbol (Example: T = 7 ) is not a standard apostrophe, but is a “Grave Accent” and is found on the tilde (~) key Also keep in mind that the use of /-/ for H for example, aren’t used nearly as often as the normal letter in a quick conversation.
To write an entire sentence this way would take three times as long, thus the quicker single symbol or letter substitutions are more often used.