The reason their are so many is because everyone wants a get rich quick scheme.
I think a major reason is "excessive early adopter awards", a problem we discussed in a previous thread called the "Coin Complaint List" (https://bitcointalksearch.org/topic/coin-complaint-list-183256).
Most of the altcoins are either premined or designed on purpose to give huge rewards to the early adopters but ever-decreasing awards after that. Consider Bitcoin itself. Half of the coins were mined between 2009 until today (4 years). That leaves until 2040 (27 years) to mine the other half of the coins!
The only way with this design to be a privileged insider is to be the one starting it, or at least get in on the ground floor. So people start currency after currency, then will probably lose interest once the rich mining rewards stop, and they'll be on to the next one.
I would recommend that some future coin incorporate a constant rate of coin creation because of this. Each year, the coin could create the same exact amount of coins as the year before, say, 1 billion coins per year or whatever. That would give newcomers the same opportunity to mine coins as early adopters. This would seem to give the currency more staying power, since you wouldn't have to dump it just to get in on the ground floor of some new currency where you are the privileged few. Also, the rate of inflation would steadily decrease over time, so I don't think it would be a problem. Unlike national currencies, at least the inflation would be predictable (assuming that the usage of your coin is constant or growing).
