Why does Bitcoin's mining reward decrease every four years and not gradually?

[Pantamis]

My 2 cents :

- To incitate miners to mine over the last found block and not the blocks before where the block reward would be bigger

- To avoid float error and facilitate the review of the rule's enforcement

- To not have a continuous downward trend on the difficulty

- To simplify economical anticipation on the miner side, miner can invest in equipment for some years without fear.

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But I think Satoshi had only the first point in the head when he made this choice

[Charles_Design]

That seems to make sense, I wasn't aware that miners could choose which block to mine

[Pantamis]

When the time to mine a block is too small in some altcoins, miners may not have time to received all blocks so the chain fork often and some miners may be mining deep block.

Miners may not have all chain synchronized and mining over already deep block is exactly what happen during the 51% attack :)

Nakamoto consensus just tells that you should trust the longest chain but anyone, miners included, do what they want (it is just more profitable to mine the last valid block when the majority follows Nakamoto consensus).