Why does my iPad show as in a location 35 miles away?

I’d make an educated guess that you perhaps have a WiFi Only model iPad.

Unlike your iPhone and WiFi & Cellular models of iPad, WiFi Only iPads do not have any GPS location capability with which to directly determine their location - and as such are completely reliant upon their network connection to infer an approximate location.

Your approximate geographic location would be estimated from a “database lookup” of (a) your WiFi Network Name (SSID) or detected neighbouring WiFi networks - and (b) the “public” IP Address provided by your Internet Service Provider (ISP). 

If the mapped WiFi network name or IP Address are not available within the applicable databases, or if this information substantially differs between sources, then your approximate location may not be computed. This situation often occurs if you are in a remote/rural location where neighbouring WiFi networks are scarce - or if connecting over satellite or VPN connections.

Network IP Addresses and WiFi networks are frequently mapped in urban and cosmopolitan areas (including “crowd source” techniques) and as such approximation of your location from lookup against these databases can be provide relatively high accuracy. As population and network density diminishes, this mechanism becomes progressively less reliable.

If you can, perhaps try connecting to a different WiFi network - be it private, public or your telephone WiFi hotspot.

I hope this explanation as to possible cause is helpful.

Because it doesn't have GPS and your location can't be triangulated using cell towers.