Supply control. The more miners you have mining it, the less control you have over the coins, as well as the market pricing. When blocks are very small, and you can only mine with CPU/GPU, you won’t see a flood of coins coming to market at any given time. Moreover, it stretches out the mining period to potentially a lengthy number of years, depending on the block size and the total number of coins being minted.
Basically put, GPU mining rigs are very expensive to operate, and if the blocksize is small, you probably are not going to be able to mine effectively. I have seen 3 Euros per coin price out there. That’s all well and good, but if you have 5 coins per block and solving a block takes too long, you may end up spending more money for electricity (especially in England) than you get value from mining the coins. This is a perfect scenario for them, especially if there is ANY premine, because rarity and slow coin growth equates to value and price appreciation over time, pending there is enough demand and use for the coin.