Because that means your data is highly denormalized and has plenty of duplicates. But in all likelihood it means no one knows wtf this table actually represents and you should be firing people.
I've seen this play out. Usually the many columns is because everyone misuses the table and eventually their special little business scenario or "filter" needs to be a column. Bonus points is whoever has to reference this table, they have to copy over whatever the hell your PK seems to be, and the cycle repeats, this time a bit worse.
Last place I did a brief project in had this. Queue 1000 tables spread across 25 schemas, each table having wide PKs, 20 redundant indexes on each table, and despite all this the database performs poorly. No one can tell you what each table represents, the table names are meaningless and the same data is everywhere. In order to get anything done you have to ask a small cabal of priests that knows the processes that write between these tables. After about 10 years, a partial rewrite happens and you now have 1/3rd of the data on each side with plenty of duplicate and overlap because hey.
I feel torn, I really wanna name&shame this company as a warning to all developers thinking about working there.
