Whaaaa 100+ columns? How often do you need to add 100 columns to an existing table?
I mean honestly that has to be as rare as chicken teeth.
Haha, and yet it happens. One of the worst databases I ever dealt with was some ridiculous variant of Universal Model for a SCADA application, the databases were named D1, D2, D3, and so on; the tables T1, T2, T3, etc; the columns C1, C2, C3, you get the picture I hope...when they hit maximum column count they would create a new table and bizarrely rebalance renumbered columns between them. In database D0 there was a catalog with all of the details relating back to the actual model. The system was actually implemented at some defense contractors and power system operators, I remember someone at Lockheed whining about hitting the number of databases limit for Sybase.
Hopefully nobody has to deal with that crap any more.
Adding new columns by creating a new table is easy and cheap and doesn’t involve downtime. Adding 100+ columns to an existing table because the spec said a relationship went from 1:0-1 to 1:1 is a pain.
(This can be avoided with creative design with deferrable constraints, something certain major RDBMS are still lacking, gah!)