The advantage of review scores is that you can analyse huge datasets with numbers and filter / sort / exclude games by scores.
For example I wanted to know, how many Steam games with at least 70%, 75%, 80%, 85%, 90% SteamDB-Rating are already marked as Steam Deck compatible.
No problem thanks to a SteamDB rating slider in the Steam Database:
Wouldn't have worked with reviews without a score but only pros and cons.
Wouldn't have been that detailed with only three categories (good, average, bad).