Because the time between looking at the list and accepting the quest can be arbitrarily long there is the question when to do the proximity check: Optimally it should be done when accepting the quest and doing the reset but then it can happen that you want to accept the quest and the GUI won't let you. That would be confusing to the player, even with an error message.
If you do the check when the player accesses the quest list, there are small drawbacks:
1) In the meantime a player could have driven there, so the reset at accepting the quest can still be observed sometimes.
2) There is a small exploit possibility: It allows selecting quests by exiting the selection screen and a friend driving to the POIs offered so the selection has to change.
3) A dynamic list looks like a bug. There was a quest there, next time you look it vanished, next time it might be there again. Huh?
Those three small drawbacks are very small and the chances of them happening are very little.
"1) In the meantime a player could have driven there, so the reset at accepting the quest can still be observed sometimes."
Having someone witness a POI reset 1% of the time is much better than 100% of the time. Like I said though, it's not perfect, just much better than the way it is now.
"2) There is a small exploit possibility: It allows selecting quests by exiting the selection screen and a friend driving to the POIs offered so the selection has to change."
The missions and their distances might be listed when looking at it, but their exact locations are unknown until you accept them. Maybe after playing a map for a long time, would you know that there is only one of a particular POI to attempt to do this, but in this case, perhaps #3 could step in.
Just want to say that if having a friend drive to a location on the list is an exploit, then the double dipping in its current form is also an exploit... just an easier one. So, even if this did not solve the problem fully, it still reduces it significantly. You always have at least one person wasting a whole lot of time who could be doing something more productive for the group.
"3) A dynamic list looks like a bug. There was a quest there, next time you look it vanished, next time it might be there again. Huh?"
In most games with missions that cycle, there is a timer in between mission list changes. This doesn't necessarily mean a mission you accepted a minute ago is no longer active, it just means that there is a new list of available missions. In fact, doesn't this already occur for the goods a trader offers? The concept of dynamic mission lists is far from new, and for some gamers, even expected. However, changing them to red, or graying them out, or marking them as temporarily unavailable is always a possibility if confusion truly is a problem.