Except you will stop anyway though then we would have 25 Bitcoin block rewards for some years from now and then suddenly only fees anymore. No time to adapt. Which most probably would break bitcoin.
The theory teaches us that the amount of money in circulation should correspond to the amount of goods being produced and traded. So far the best way of doing just that is by creating (and destroying) money through credit (but it is ostentatiously vulnerable to abuse by the powers to be)...
No fixed algorithm like halving can do such a trick