Russia Ukraine war, page-238213

To surprise and try to put pressure on Kiev. Get a stronger hand in the negotiations that were underway at the time.

Why Kherson is easy: one of the main gains was related to control of the North Crimean canal and source. Re-establishing the water flow was good news for Crimea for awhile.
Zaporizhia: part of long term defense of the east. It worked pretty well last year.

I doubt there are many left who still pretend it isn't a proxy war. You're one unique specimen.