Does size of Time Machine backups increase after changing from HDD to SSD on a Macbook Pro?
I suspect this has something to do with the way SSDs work, specifically something about SSDs having to rewrite huge sections of memory even if only a part of the section needs to be changed.


This happens at the storage and controller level - it is completely transparent to the operating system.

You have already found the main cause, but one thing you didn't notice was that the day after you changed your drive, Time Machine did a complete backup from the beginning. TM noticed a new device ID on the drive and made a new backup. It is possible to join backups IF you do it before the first run after the drive change, but it involves some tinkering in the Terminal.