Since a couple people mentioned the hydraulic TVC, that's my bet as to what went wrong, or at least contributed to it.

After two minutes of flight with the heat of 33, I mean 27, I mean 26, errrr, 25 engines*, the hydraulic fluid might have boiled and that was the end of that - it had the directional stability of letting go of a balloon.

What absolutely amazes me is that this is the very first time a Starship booster has ever left the pad, and it was done under full fuel load and worked for nearly its entire flight profile!

O2

* I noted several occurrences of engine-rich exhaust during its flight.