Anyone investing in altcoin for the reason of diversifying is doing it all wrong as this is the worst market to diversify in as the market is highly volatile and totally depends on each other and Bitcoin the most to survive. Reason you should Invest in altcoin is because of the technology it is working on. We have quite a number of project working on very promising technology that could be life changing technology in the future and getting to be among the first believers could be of great advantage.
Just imagine the early adopters of good project like uni swap and how profitable they are today provided they held their coins from the very beginning. Altcoins could be very promising if you picked the right project to invest in.