First of all, I apologize, but I don't think the developers of Heroes are any less intelligent than you are. If they made it this way initially, there was probably a good reason.
The idea of setting a limit on turns on the map, but not on battles, must have come to one of the developers while they were very hungover, because I don't see any clear reasons for it. There are also no analogues of this in other competitive activities with time control.
Therefore, as soon as a more or less acceptable tool appeared in the form of WOG, the idea of creating a normal timer came to the community quite quickly.
Secondly, battles and chains of actions are simply different things, at least in terms of the amount of time they take. Chains of actions can and should be planned in advance, for example, during the opponent's turn.
By the way, personally, I would prefer the opposite - unlimited time on the map and time control in battles. Because battles are 90% or more typical, the number of options is limited, and almost all of them have been practiced countless times in games.
But actions on the map have a much wider range of options, plus they strongly load the intuition, the quality of which noticeably depends on the amount of time available for thinking.
