The warning you receive when a formula is not consistent is a nice feature, and an advanced user will quickly learn to be very sensitive to those warnings, will spot them quickly, and avoid causing them when possible.
To strictly enforce that the formula must be the same in each cell of the column would not be very excel-like, I can't see it being done.
Yep, the problem is that I have this conspiracy theory that Microsoft has designed Excel to be the ultimate booster of Dunning-Krueger effect so that most people think they are advanced users [1] while they actually have no clue what they are doing. All the while giving no protection whatsoever against those Dunning-Krueger cases.
To strictly enforce that the formula must be the same in each cell of the column would not be very excel-like, I can't see it being done.