A lot of people who aren’t AoE III fans yet have got problems with the cards/shipments from the home city. Especially AoE II fans are not used to be able to get ressources (etc.) from outside the map itself.
In AoE II, memorizing the applying tech tree can be hard. Even pros like Hera check from time to time the tech tree during a game (he for instance did during the last NAC finals). The full tech tree gamemode makes this very easy for beginners. It’s hardly used, but it’s there for those who like it or want a change, just like using for once cheatcodes in single player.
Some are against such a “no cards” gamemode because they are such a huge part of the game. In fact some civs. are even specialized in it (like the Germans or Spanish). But this is also true for the “full tech tree” gamemode in AoE II ! Some civs. are “specialized” in having a wide open tech tree, like the Byzantines, Chinese or Saracens (except for the missing cavalier upgrade, which is bad, the Saracens actually have a much more open tech tree than the first two mentioned civs.).
I believe a “no cards” gamemode could attract more interest from AoE II players to try AoE III out, if one huge (if not biggest) change can be removed. The beauty of an extra gamemode being of course, that it doesn’t change anything for the usual fans. They, me included, can just ignore that gamemode, like AoE II’s “full tech tree” is mostly ignored (me included, although having Persian elephants w. heresy is pretty cool).