Why is the VPN switch sometimes missing from settings on my iPad? There is a VPN switch in settings that often appears below the wifi option in settings on iOS: 

(the above image is from a website and not my iPad, as I can't seem to get my iPad to show VPN right now)

The trouble is, it seems to be missing:

(this image is from my iPad)

VPN switch present:


in all circumstances prior to installing an AT&amp;T sim card, including when a Telus sim card was installed
while using wifi with an AT&amp;T sim card installed but in a region with no AT&amp;T coverage and no data roaming disable by AT&amp;T (ie. "searching..." shown in connection status area)


VPN switch missing:


while connected to AT&amp;T LTE/4G using iPad sim
while connected to my AT&amp;T iPhone using personal hotspot (via either Bluetooth or wifi) even though VPN is available from the settings screen of my iPhone whether or not cellular data is enabled on iPad
while connected to WIFI whether or not cellular data is enabled on my iPad


What is going on here?  Does the connection/sim card/network somehow determine whether VPN is available?  Is there something else altogether I need to check?
Check for a VPN Profile
Turns out the missing VPN switch had nothing to do with which connection was used.  What seems to have happened is that all the VPN profiles were deleted.  When that happens, the VPN switch seems to disappear.  To check for or create a new VPN profile, go to settings-&gt;general-&gt;network-&gt;VPN:

Once you create a VPN profile, the VPN switch reappears in the root of the settings screen: