Well altcoins made several people earn and keep making people earn insanes ammounts with it,soo thats why they keep and will always be.The main fact is all altcoins has the xxx/uᴉoɔʇᴉq .I believe if were only uᴉoɔʇᴉq we could see some manipulation at the uᴉoɔʇᴉq value ,and well less people thinking its a scam project,but well altcoins are supporting the uᴉoɔʇᴉq earnings.
I think altcoins just preventing bitcoin to evolve and grow maybe i am not right but that's what i am thinking.
With the help of alt coin bitcoin can integrate some part of other alt coins so that bitcoin can evolve in to a better coin.