Convincing those that don't understand this to spread their value among multiple cryptocurrencies meant for the exact same purpose so obviously goes against the goal of gaining sufficient trading depth of one.
I think the problem are lost coins.
Since the immature operating systems people loose them from time to time.
The figure is probably very small but I think it's significant with a reason:
At first if there is a perceptual loss of coins over time they will eventually
in correlation with the pigeon-principle all be lost.
Another one is the psychological factor. If somebody has started mining early and lost coins this is more traumatizing as being robbed, loss due to speculation in the old money or the outcome of unprofitable mining at current difficulty. The realization that the profit will be gone forever has much deeper implications. It may be comparable with a destroyed property.
So this person may try by any means to get it back but since this isn't possible anymore there has to be new ground.
To compensate for this factors new crypto currencies must be created over time.
Just my humble theory...
Yes it could really be that the makers of these alternate currencies are just jealous of the pioneers.