Why don't treasure maps stack and why can't you have more than one of the same map on you?

CrashTest

Also, why can't you put them in guild bank but you can sell them in guild store?

twev

They're designed to take up room, requiring expenditure of time and effort to redeem for the 'loot' they contain.

If they stacked, or were easy to move around - you'd hoard them until you had enough to run in and scoop up many at one time, which would take a lot less time and effort. That would defeat one of the basic design parameters of 'the game', which is to occupy as much of your time doing stuff as possible without requiring them to design maps and delves at a faster rate than they already have to.

Surveys are slightly different, in that it's just raw materials that you have to either refine and use/sell fairly quickly if you dont want to be 'forced' to pay for ESO+ so you could store endless amounts.

Refining the materials efficiently that you get from surveys requires you to grind levels and points to invest in skills, and that takes time and effort as well, so you're burning up time/effort keeping busy, which is one of the design parameters as mentioned above.

The game is enjoyable for many reasons, but it's supposed to use your time, not be efficient.
If it was too efficient to accomplish goals, you'd be done and move on to some other game, and they need you to stay here populating this one.

Greydir

Both, treasure Maps not Stacking and not being able to be put into a guild bank, are because of past bugs / exploits either removing them all instead of on if you got to the location or them being able to be used for item multiplication if put in guild banks.

Since posting the function of exploits (I think even fixed ones) is against the ToS i can not further elaborate on that. It was possible, and people got banned for the duplication of surveys and treasure maps. I think it was around the release of orsinium or something like that, so years ago.