Let me know if my theory is correct
heres how: Because there is a restriction on the amount of coins produced, you need as few people as possible to mine the same coin as you. if half the people are mining these "crapcoins" and the other half are mining LITECOINS it means its easier for you to make money mining litecoins. if these half wernt mining the "crapcoins" then they will be mining litecoins and your earnings are halved, as the difficulty will be twice what it is now.
Think of these new coins, that many times have a higher profitability than LTC, as a tool to get more LTC than you would have mining LTC.