This is called progress. In y'olden days, our car clocks used to be set from FM-RDS (which in this country corrected for GMT/BST), or DAB (again, corrected for GMT/BST). In rare cases, the car clock could be set from the 60kHz MSF (ex-Rugby) UK Radio Clock signal, transmitter at Anthorn, Cumbria.
Now, our new cars get their time signal from GPS - which of course, has no concept of Wintertime or Summertime! Hence no automatic correction for GPS time based signals.
In fact, GPS is actually 16 seconds out from UTC (due to leap seconds), see here for more info:
http://www.audi-sport.net/xf/threads/time-change-to-bst.213816/#post-2126848
so the GPS receiver in the car needs to correct for this 16 second variance.
So - in order to "fix" our cars for automatically changing BST, they need to either
Reference FM-RDS again
Reference DAB again
Reference the 60kHz UK Radio Clock
Or insert rules into the software (Last Sunday in March +0100 at 0100, Last Sunday in October -0100 at 0200)
Simply put - because our cars get their time from GPS - GPS has no concept of Summertime/Wintertime.