There's always a reason for a dev to ship something shitty but when you show you can use 80% less storage for the same operation you can make the accountants your lever.
But I don’t think that’s the top 5 reasons of normalization
1NF removes repeating groups, putting for example data for each month in its own row, not an array of 12 months in 1 row.
Storage efficiency was never the point. IMS had that locked down. Succinctness of expression and accuracy of results was the point. And is: normalization prevents anomalous results.
Normalization ultimately boils down to breaking your data down into the most elemental and simplest "facts" about them, and its greatest value is how it allows and encourages more flexible and disparate ways of looking at the same information.