Most of these are in a metal box, which blocks signal. Adding careful routing to get an antenna in an unshrouded position where it's still physically protected is a pain. Also, in the middle of an apartment building can give you pretty terrible reception in the first place.

GPS doesn't provide time zones or daylight savings info. The appliance would know where you are and what UTC time it is, but not which time zone you're in. The manufacturer could pre-program shape files in (yay, more memory) but they become obsolete the next time a politician decides to move time zones or change daylight savings. If this happens to you, your device will keep repeatedly changing to be an hour fast/slow no matter how often you reset it.

You could have the GPS satellites continually broadcast shape files for the time zone but this would be a big change, use up a lot of the limited bandwidth, and it would take your clock half an hour to set itself.

it's like an extra $5-10 in parts and unlike a WiFi module, the manufacturer can't make any big data or ad revenue from it.