Sometimes it's just to shorten a text, sometimes it's to make the text clearer, and sometimes it's to change how the card works so that they are less powerful.
Goyo Guardian is an example of the last one, it originally can be summoned using any Tuner. But a generic synchro with 2800 ATK and monster stealing effect was later on deemed too powerful as newer cards that can easily abuse it shows up. As a result, it had to be banned.
However, much later on they decided to make the banlist slimmer. This leads to some banned cards receiving an errata to make them less powerful so that they can be released from the banlist.
Goyo Guardian is one of such card, having its summoning condition changed into requiring EARTH Tuner, making it less generic.
Anoymous
Tackrad