It is simple, it is through Altcoin you can easily multiple your money, for BTC to do X2 from the present price is bid deal, but very easy to see Altcoin do 2X, 3X in a matter of weeks
This is mainly the correct answer. But the side effect of this is that altcoins are worth something. Since people merch them up or pump and dump, it makes them worth "something". We probably don't all agree on the worth of almost any of them.
I agree some are worth a few dollars each and have great use cases. Others are people testing out the next best thing, and since people buy and sell them for profit it empowers the creators to fund themselves. When a new coin comes out and they premine it they use those funds for paying people. It is interesting that they can generate wealth from almost nothing like that.